Mix 1 part peanut butter
1 part plaster of paris (cheap at any craft store)
Mix with vegetable oil until very thick paste forms DO NOT USE WATER
Roll into balls and place where mice or rats have been seen or feeding. I also put some under my coop. If I do this inside the coop I put the balls under a milk crate with a large rock on it so the chickens can not get in but the rodents can. The mice/rats eat the mixture drink water and the mixture turns into concrete in their stomachs and they die.