When my dad recently laid down concrete for the foundation for a new grain dryer he was told to first break up glass bottles on the ground all over where the foundation was to be laid. If rats, rabbits, etc try to burrow under they will be cut up by the glass. He has an older dryer that he was afraid would collapse because of all the rat tunnels under it. Thought this was a good tip for those who lay a foundation under a coop, probably even for just a floor on top of dirt.