A customer of mine is interested on insulating the underside of their house. It is stick built on a block and post foundation (not a mobile). Easy done, but my question is this; How can I / they keep mice from making a small city in the insulation and is there a cost effective product that mice wont live in?
You could try spray polyurethane foam but it is more expensive and makes the underside utiliteis difficult to access. I'm not sure what would stop mice but something like 2" polystyrene board might slow them down.
There are some type of deterrents you can use; I'd contact a exterminator and ask them their opinion. I'm sure they deal with that situation all the time and need to prevent future issues with that exact problem.