Every summer here the snakes become more active and people panic, killing or removing green racers, kings, gophers and rattlesnakes. Then the mice move in and they wonder why. You want a mice free home?- Get a Boa Constrictor. If you take a torch at night and have a look about in the dark house you can spot various cracks and openings in the plumbing, electrical lines etc. that mice use. If you can see light going through , so can the mice! Get some steel wool and pack the holes using a long darning needle or similar tool.