I had a similar problem when we moved into an old house on an even older golf course that abuts the everglades. we were killing 5-9 mice a day with my sheridan pellet gun. at some point they moved away. mice are smart I guess. i kind of miss them they were fun to shoot. it got to point where my son and i were betting on which eye we would hit. first get a pellet gun then cats would be my suggestion. curval is correct cats don't need to be indoors and feed them just enough to keep them around that way they'll hunt.