Between farming and driving an LP truck I've tried about anything that was handy.  Nothing beats plain old wasp spray.  Gasoline works but there is that slight fire/explosion problem, electrical contact cleaner and brake cleaner work well but can be hard on paint.  Soapy water and leak detector solution work, but I just don't have enough faith in them.

And wasp spray works on dogs as well.  Doesn't kill them but they get really sick really quickly.  Much better than pepper spray, which just makes some dogs angrier.