You could always get a bigger dog.

Are you feeding the cats or did the people before you feed them? Is there some sort of food source for them? There must be some reason the cats are hanging around.

If you can't find a reason maybe a quit shot of water would work. Keep your hose handy or buy a good squirt gun and just give them a shot of water. I don't think anyone will turn us in for animal cruelty for that.

Devildog

No I do not feed them neither did the people that had lived here before. The cats belong to others in the neighborhood that let them run loose. I have 3 cats myself, but they are all kept indoors. When my cats are laying on the window sills the others come around then my cats want to fight with them through the screens. I dont' want to get a dog right now, so the water bottle is a good idea. Thanks