Cat Piss.

We have a traveling vet that does neutering for $50/, Dirt cheap. Neutered cat won't pee in your car, and IF he is a fighter, he will keep the other Toms away.
A farm neighbor had another neighbors tomcat come over and fix up his females. He had to find homes for the kittens. One day he had been nutting the yearling bulls, so he had the antiseptic and scalpel in hand when the tom cam by. He picked up the tom and kicked his rubber boot off. Stuffed the cat head first into the boot and nutted him. Said he turned out to be the best mouser he had. Tom never left after.