logbook,

Dumb question, but I think it may be relevant: Where exactly do you park your car? In a garage? On the street?

If you do have a garage, you might want to make sure that your garage is fairly rodent/bug proof. Keep your garage doors shut as much as possible and make sure that you keep the surrounding area clean as possible, to deter rats and other vermin from coming back.

Out on the street, it may be a litte more difficult. Again, try to keep the area around your vehicle as clean as possible; i.e. no food to attract vermin.

You might also want to place rat traps/poison right around the spot where you usually park your car.

Deterrence is still the best way to avoid problems like yours (simply by keeping things clean), but if all else fails, the traps/poison should proactively solve any issues.

Good luck!