Are your cats altered pixie? If they aren't that may help the situation.

I agree though, the other cat needs to be castrated.

I think scaring him off would help, but certainly don't hurt him. I understand how you feel, but animals are animals. This is there instinct, dominate or be dominated. He probably did not penetrate unless one of your cats is in heat. I don't know about cats as much as dogs, but a dog will not penetrate unless the female is in heat.

They also make a spray that they sell in the pet stores that will keep a cat from spraying. If he has sprayed your yard you will want to hose off really good and then spray the deterent.