You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to devices which prevent unauthorized access to ladders. More particularly, it relates to a modular device that attaches to a ladder obstructing access preventing children from accessing the rungs of the ladder. 
         [0002]    Ladders create an attractive nuisance because young children perceive ladders as obstacles or toys which are to be climbed upon but the ladders present dangers that are not fully comprehended by young children including falls and access to dangerous and equally enticing areas such as swimming pools or spas. While parental supervision and fences can help prevent accidents, ladder guards can provide an additional layer of safety by deterring a child&#39;s attempt to climb. 
         [0003]    Previous attempts at preventing unauthorized use of ladders include ladder rung covers and complex folding rung mechanisms. These devices and methods, however, can be cumbersome, difficult to use, complex and/or prohibitively expensive. 
         [0004]    Ladder rung covers are generally single panels that are clamped, bolted or strapped or hinged to the ladder. The guards block access to the rungs, preventing a person from using the ladder. The cover&#39;s size weight and fastening mechanisms can make it unwieldy and cumbersome for a person to attach and remove and once removed, must be secured in a safe location to prevent stumbling upon or damage. 
         [0005]    Folding ladder rung mechanisms also can prevent unauthorized access, however such mechanisms can be expensive to construct and maintain with multiple moving parts. Such mechanisms are not readily adaptable to existing ladders, thus require entire replacement of the ladder. 
         [0006]    Thus there exists a need for a ladder guard that can easily be attached or detached by an adult, but prevent small children from accessing the ladder, that possesses no moving parts, can be adapted to existing ladder systems, and once removed can be left in or near the ladder without presenting a danger to others. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The disclosed ladder guard is secured between the rungs and stringers of the ladder to prevent use of the rungs as footholds or handholds and deter ascension of the ladder, especially by children. The invention is comprised of a compressible material of a desired resiliency allowing an adult to deform the invention for insertion or removal between two adjacent stringers. The left and right sides of the invention completely or partially surround the left and right stringers of the ladder to deter the invention&#39;s dislodgment by the would-be ladder user. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention is illustrated by the accompanying drawings, in which: 
           [0009]      FIG. 1  is a perspective view of three units of a first embodiment of the invention attached to a typical pool ladder. 
           [0010]      FIG. 2  is a perspective view of the first embodiment of the invention showing the invention partially compressed for insertion or removal. 
           [0011]      FIG. 3  is a front perspective view of the first embodiment of the invention. 
           [0012]      FIG. 4A  is a front view of the first embodiment of the invention. 
           [0013]      FIG. 4B  is a top view of the first embodiment of the invention. 
           [0014]      FIG. 5  is a bottom perspective view of a second embodiment of the invention. 
           [0015]      FIG. 6  is a perspective view of the second embodiment of the invention. 
           [0016]      FIG. 7A  is a front view of the second embodiment of the invention 
           [0017]      FIG. 7B  is a bottom view of the second embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The drawings illustrate an invention that enables an individual to restrict access to a ladder, especially to restrict a child&#39;s access. 
         [0019]      FIG. 1  shows a first embodiment of the present invention in the form of a resilient modular ladder guard  10  attached to a typical above ground pool ladder  2 . While a typical pool ladder is illustrated in the following figures, it should be understood that the invention may be employed with any ladder having a rung  4  and stringers  6 ,  8 . 
         [0020]    The modular guard  10  is placed between two adjacent rungs  4  of the ladder  2  to prevent a small child from easily climbing the ladder  2 . The module  10  is modular and the number of units can be increased or decreased depending upon the number of rungs  4  of the ladder  2  needing to be obstructed. Preferably, each unit is constructed of a resilient foam material. The height of each unit is sized to fit the intended ladder, or can be cut to fit by the end user to fit the particular ladder&#39;s rung spacing. 
         [0021]      FIG. 2  shows the module  10  as it is being installed upon the ladder  2 . The module  10  fits between the left stringer  6  and right stringer  8 . The module  10  possesses a left invagination  30  such as an indentation, crevasse, fold or slit on its left side  12  and a right invagination  32  on its right side  14  that allows the left side  12  to receive the left stringer  6  by extending past the left stringer  6  medial surface  7  and allows the right side  14  to receive the right stringer  8  by extending past the right stringer  8  medial surface  9 , preventing the module  10  from becoming dislodged by pushing on its front surface  16  or rear surface  18 . Here the invaginations  30 ,  32  are shown as slits cut into the left and right sides  12 ,  14  and extending from the top surface  20  to the bottom surface  22  providing a passageway that accommodates the left and right stringers  6 ,  8 . The invaginations, or slits  30 ,  32  extend toward each other a sufficient amount to allow each unit  10  to be positioned between the stringers  6 ,  8  of the ladder  2 . 
         [0022]    Insertion or removal of the modular unit  10  requires compression of a side  12  or  14  or portion thereof of the unit  10 . The material each unit  10  is constructed of provides sufficient resistance to compression such that a typical small child would not possess sufficient strength to dislodge the unit  10 , but is sufficiently compressible or flexible to allow an adult to compress and dislodge the unit  10  with moderate force. Here a portion of the left side  12  is compressed. The compressed portion  13  allows the unit  10  to rotate about the right stringer  8  and subsequently be removed. 
         [0023]      FIG. 3  shows a perspective view of the module  10 . The module  10  preferably possesses an elliptical or oval horizontal cross section as viewed from the top surface  20  or bottom surface  22 . The horizontal cross section could also be square, rectangular, octagonal or other desired shape. Here the invention is shown having an elliptical horizontal cross section with the major diameter oriented generally parallel to the width of the ladder, the invention possessing straight vertical left, right, front and rear surfaces,  12 ,  14 ,  16 , and  18 . The elliptical cross section discourages individuals from grasping the corners of the invention to aid in climbing. 
         [0024]    The left invagination  30  begins at the left surface  12  and extends inward terminating at a left cylindrical surface  40 . Likewise the right invagination  32  begins at the right surface  14  and extends inward terminating at a right cylindrical surface  42 . The cylindrical surfaces  40 ,  42  and indentions  30 ,  32  extend from the top surface  20  to the bottom surface  22 . The cylindrical surfaces  40 ,  42  are shown here as having a circular cross-section forming a cylindrical shaped aperture extending from the top surface  20  to the bottom surface  22 , but may alternatively have other cross section including an elliptical cross section, that form a complimentary fit with the stringers of the ladder. 
         [0025]      FIG. 4A  shows a front view of the module  10 . The walls of the cylinder holes  40 ,  42  extend from the top surface  20  to the bottom surface  22  and are shown by the hidden lines. 
         [0026]      FIG. 4B  shows a top view of the invention showing the upper edge of the left surface  12 , right surface  14 , front surface  16  and rear surface  18 . The left invagination or slit  30  extends from the left surface  12  to the left cylindrical surface  40 . The right invagination or slit  32  extends from the right surface  14  to the right cylindrical surface  42 . 
         [0027]      FIG. 5  shows a second embodiment of the invention having a recessed cutout portion  50  in the bottom surface  22  of the module  10 ′. The recessed portion  50  allows the outer surfaces  12 ,  14 ,  16 ,  18  of the invention to completely enclose the ladder rungs  4  of the ladder  2 . While a recessed portion  50  is shown in the bottom surface  22  of the unit  10 ′, a recessed portion may also be located in the upper surface  20  or both the upper surface  20  and lower surface  22 . 
         [0028]    The recessed portions  50  allow the upper surface  20  of a first unit to mate with the bottom surface  22  of a second unit without significant deformation, discouraging a person from using the upper surface  20  as a handhold or foot hold to climb. 
         [0029]      FIG. 6  shows the second embodiment of the module  10 ′ attached to a ladder  2 . The middle unit  11  is shown compressed for insertion or removal into or from the ladder  2 . The recessed portion  50  minimizes or eliminates any gap between the upper surface  20  and lower surface  22  of any adjacent units  10 . 
         [0030]      FIG. 7A  shows a side view of the second embodiment  10 ′ of the invention with hidden lines showing the cylindrical surfaces  40 ,  42  and the vertical wall surface  51  of the recessed portion  50  at lower surface  22 . The recessed portion  50  forms a cavity that may enclose a ladder rung  4 . 
         [0031]      FIG. 7B  shows a bottom view of the second embodiment  10 ′ showing the recessed portion  50 , left invagination slit  30  and left cylindrical hole  40  and right invagination slit  32  and right cylindrical hole  42  and bottom surface  22 . The recessed portion  50  of the lower surface  22  is shaped to allow the ladder rung  4  to preferably fit within the cavity of the recessed portion inner surface wall  51 . 
         [0032]    The ladder guard invention&#39;s preferred construction from a compressible foam material creates a device that is lightweight, buoyant and durable. Such characteristics allow it to be used as a toy or otherwise handled roughly with a minimal concern for damage to the unit or injury to others.

Summary:
A ladder guard secured between the rungs and stringers of the ladder to prevent use of the rungs as footholds or handholds and deter ascension of the ladder, especially by children. The ladder guard is constructed from compressible material of a desired resiliency allows an adult to deform the invention for insertion or removal between two adjacent stringers.