Put in self-closing doors that open outward, and use latches or spring locks to keep doors closed. Check to see that doors and windows close tightly, and use metal screens on all windows that are kept open. Cover the edges of doors, windows and screens, which can be gnawed, with sheet metal or hardware cloth. Make a collar around pipe and wire openings into the house with pieces of sheet metal or tin cans. Rats cannot easily gnaw through metal.
Fasten floor drains tightly to keep sewer rats from coming in.
The two best ways to remove rats are traps or poison. Choose wooden base snap traps, and enlarge the traps by fastening a 2-inch square of cardboard to each trigger. Set out several traps at a time - at least 10 if you think there are many rats. Place the traps behind boxes and against walls, so that the rats must pass over the trigger. Fasten food attractive to rats, such as peanut butter, raisin bread, bacon or gumdrops, tightly on the trigger of each trap.