[Tcoat]

This has come up here a few time and although loads of things were brought out (mothballs, rubber snakes, ultrasonic noise generators, etc) nothing seemed to work as well as some good old rat poison. Just get the stuff that dries them out and place it near where you park (not in the open where pets can get it though). Since it makes them thirsty they head away looking for water and should not die in your car (check every few days anyway just in case).