I keep 6 chickens in a pen that my husband made in one of the horse stalls in our barn. There is a sliding door that can be closed at night, and the rest is all fenced in. It has pine bedding on the dirt floor, and the barn is a metal building. He built roosts and nesting boxes on the wall, and it is real nice, except we are having problems with mice now that it is cold here in Kansas. Any way to cut down on their population without hurting my chickens?