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BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    This disclosure relates to screens which block rodents, snakes and other wildlife. Specifically, this disclosure relates to screens for drainage holes in concrete block walls. 
         [0003]    2. Background Art 
         [0004]    Block wall construction is common in many areas as a privacy fence for residential and commercial properties. When a block wall is built, a common method of facilitating drainage of water from the area is to place some of the blocks on their side at ground level so that water may flow through the openings in the blocks. This method allows drainage of water, but also allows creatures small enough to pass through the holes to enter the area enclosed by the block wall fence. These creatures include snakes, rodents, and insects. As this method of privacy fence construction is common in the desert, scorpions also may enter an enclosed area through the drainage holes. The enclosed area may also be used to keep pets, and some pets may be small enough to escape through the drainage holes. 
         [0005]    One way to prevent larger rodents and snakes from entering, and some pets for exiting an area enclosed by block wall fencing is to place rocks in front of the holes. This method has drawbacks, as rocks are heavy to move and place and some animals are able to move the rocks enough to get through the drainage holes. Also the rocks partially block the ability of water to drain, and in some cases may prevent proper drainage. The rocks may not prevent snakes and other creatures from entering the enclosed area. Further if the block wall is also a retaining wall, then the high side of the wall the drainage hole may be at ground level, and on the lower side of the wall the drainage hole may be above ground level. It may not be practical to pile rocks high enough to cover the drainage hole on the lower side, as it may defeat the purpose of the retaining wall. Also a person desiring to block the hole from creatures may not have the property rights necessary to pile rocks on the high side. 
         [0006]    Another method of blocking the drainage hole is by use of a screen. Screens have been employed in combination with rocks to hold them in place. They have also been employed using anchors mounted in the block wall to hold a screen in place. There are some advantages in using screens over rocks, such as increased water flow and superior protection against snakes and scorpions. When using a screen with rocks, however, the screen may be moved by animals, and the rocks may be moved by erosion, or by animals, providing a gap through which creatures may pass. When a screen is used with anchors, the anchors must be installed in the block wall without damaging the wall. The anchors may become lose over time if installed in the mortar between the blocks. With either method using screens it may be necessary to cut the screens to the proper size, which is a time consuming and difficult process. The process of installing the anchors in a wall may also be difficult and time consuming. 
         [0007]    There exists a need for a screen which is quickly and easily installed to block a drainage hole in a block wall from the passage of animals and creatures, and which can remain in place despite the forces of erosion, and despite the attempts of animals to move them. 
       BRIEF DESCRIPTION 
       [0008]    The blocks in a block wall often have two holes, and when a block is turned on its side for drainage purposes there are two holes for drainage, with a center part of the concrete block between the two holes. In an embodiment of the invention a screen for a drainage hole may have a frame which clamps, or holds using tension, a screen in place in a drainage hole. The screen frame may clamp around the center part of the concrete block, the frame providing support for a screen blocking the two holes from the passage of creatures. This embodiment of the invention may be installed quickly, by simply pushing the frame around the center portion of the block. The frame may hold tightly to the center part, preventing any creature from pushing the screen and gaining access through the drainage hole. Installation of the embodiment of the invention may be done without the need for tools, making the process quick and easy. 
         [0009]    In some cases a block wall is built with a drainage block which only has one hole. In an embodiment of the invention, a screen may have a frame which is inserted partway into the hole, which contacts multiple parts of the inside of the drainage hole to provide tension. This embodiment may also be installed without the use of tools, by pushing the screen into the drainage hole. The screen is held in place by tension and friction. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a front view of a block wall showing a drainage block. 
           [0011]      FIG. 2  is a front view of an embodiment of a safety screen for a drainage block. 
           [0012]      FIG. 3  is a top view of an embodiment of a safety screen for a drainage block 
           [0013]      FIG. 4  is a front view of a block wall showing an embodiment of a safety screen installed in a drainage block. 
           [0014]      FIG. 5  is a cut away top view of a block wall, cut along the line A from  FIG. 1 , showing an embodiment of a safety screen installed in a drainage block. 
           [0015]      FIG. 6  is a front view of a block wall showing a drainage block with a singe hole. 
           [0016]      FIG. 7  is a cut away top view of a block wall, cut along the line B from  FIG. 6 , showing an embodiment of a safety screen installed on both sides of a drainage block. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    When a block wall is constructed, standard size blocks are often used. Drainage holes of various shapes and sizes may be included in the wall. The drainage holes are usually a standard size hole. The present invention allows the drainage holes to be substantially covered with a screen to prevent most unwanted creatures from passing through the drainage holes. The screens may be held in place with tension and friction as they contact the drainage hole. 
         [0018]      FIG. 1  shows a block wall with drainage holes formed from a double hole drainage block  2 . The block in this example is a standard cinderblock turned on the side to allow drainage. As shown turned on the side, the block shows a center part  4 , side surfaces  6 , bottom surfaces  14 , and top surfaces  18 . The block wall also includes wall blocks  8 , and mortar  10 . 
         [0019]    An example embodiment of a safety screen  20 , designed for the standard size of a double hole drainage block  2  is shown in  FIGS. 2 and 3 . The safety screen has a frame  22 , including a clamping portion  24 . The frame supports screen material  26  which can prevent creatures from passing through the drainage block. The frame may be made from a variety of materials including, but not limited to metal, and plastic. The frame may provide a claming portion as shown in the example embodiment in  FIGS. 4 and 5 , where the flexing of the frame material in the clamping portion  24  creates tension when the safety screen is installed. The screen material may also be made from materials including but not limited to metal, plastic, wood, natural fibers, and synthetic fibers, carbon fibers, or any other know screen material. The safety screen  20  may have a clamping portion which is not incorporated into the frame but is connected to the frame, and may include springs and other parts common in clamping mechanisms. The clamping may also create a tension only on part of the center part  4  of the draining block  2 . 
         [0020]    The safety screen  20  may be installed as shown in  FIG. 4  by pressing on the center of the frame  22  so that the clamping portion fits around the center portion. The screen  26  and frame  22  may be formed to closely fit the inside of the drainage holes. The frame may make contact with the side surfaces  6 , the bottom surfaces  14 , and the top surfaces  18 , but the frame may also be formed and installed so that the only contact with the draining block  2  is at the clamping portion  24 . The frame  22  may provide sufficient support to the screen  26  so that if the only contact with draining block  2  is at the clamping portion  24 , the frame can prevent small animals from moving the screen and passing through the drainage block. 
         [0021]    The safety screen  20  of the present example is shown in  FIG. 5  installed on one side of the drainage block  2 . The safety screen  20  may be installed on both sides of the drainage hole, which may prevent animals from nesting in the drainage block, and may prevent other material from entering the drainage block and constricting water flow. 
         [0022]    Safety screens may be made to fit the size of many drainage holes including holes which are not double holes with a center part.  FIG. 7  shows a top view of an embodiment of a single hole safety frame  30 , which is inserted into a drainage block. The safety screen  30  has a frame  32  including tension legs  34 . The tension legs  34  press against the side parts  16  of the single hole drainage block. The tension legs may press against a top or bottom part instead of, or in addition to the side parts  16 . The frame  32  supports a screen which allows water to pass through the drainage hole while preventing creatures from passing. The safety screen  30  is shown installed in both sides of the drainage block, but it may be installed in only one side of the drainage block. The safety screen  30  shown may be used to fit into the two drainage holes shown in  FIG. 1 . 
         [0023]    In an example safety screen the frame and the screen are formed from metal and may be installed by pushing on the frame to force it to enter the drainage hole. The safety screen may be installed by using a hammer to quickly force the safety screen into place. The safety screen may be assembled by forming a frame to the approximate size of the drainage hole. The frame may incorporate a clamping or a tension part to hold the safety screen in place with tension, or a clamping or tension part may be added to the frame. A screen which is capable of preventing creatures from passing may be connected to the frame. The safety screen may then be installed to prevent creatures from passing through the drainage hole. 
         [0024]    The safety screen is shown in the Figures with a frame and screen which is smaller than the drainage hole. The safety screen may also be made with a frame and screen which are larger than the drainage hole and which are held against the surface of the drainage block by tension and friction as parts of the safety screen contact the surfaces of the drainage block. 
         [0025]    While the principles of the invention have been made clear in illustrative embodiments, there will be immediately obvious to those skilled in the art many modifications of structure, arrangement, proportions, and methods, the elements, materials, and components used in the practice of the invention, and otherwise, which are particularly adapted to specific environments and operative requirements without departing from those principles. The appended claims are intended to cover and embrace any and all such modifications, within the limits only of the true spirit and scope of the invention.

Summary:
The present invention provides a screen used to block a drainage hole in a wall from the passage of unwanted pets. Specifically, the present invention includes a frame a screen and a clamping portion to secure the screen in place with friction and tension.