We have found that cayenne pepper works well to deter them from the places we don't want them. It is a respiratory irritant to them, but has no effect on the chickens. We sprinkle it in the chicken food and around anything we don't want them in.
We also have one of those silver box mouse traps that can hold up to thirty mice at a time (although mice have cannibalistic tendencies when food and water run out, so we empty ours regularly). I think it is called a humane mouse trap or something like that. We put a cracker with peanut butter inside it and catch 2-3 mice a night with that. Then we just leave it alone in the chicken run for a couple of days and my son empties it out. The chickens don't bother it, except to sit on top of it when the weather is hot. It did take over a week though for the mice to figure out how to get into it.
I know that mice are just a given problem when you have chickens, but we seem to be able to keep the population in check with constant trapping and keeping things clean. Don't leave anything around that will make a good home for them. Make sure treats and food are cleaned up. Also, make sure feathers are cleaned up. They like to eat the ends, and use the rest for nesting material.
HTH!