My motor was in to have the rear shocks replaced recently, and he said mice had been living in my boot - I can't quite figure out how they got in there, as there's no obvious entry point, and they don't appear to have been anywhere else in the car.
Until recently, I had an enormous Maine Coon cat, but they learned his habits, and how to work round them to avoid him...
The peppermint oil sounds like a possible winner
