I bought this house with a terrible problem. Cats were always in my yard and you know what they left behind.
**** The answer? Red pepper, cayenne, I use the ground in the 16 oz resturant pack that I get from Sams for about $3. Sprinkle it first where they poop, then on the fence where the cats walk and all around the edges of the yard the thickest. Then if there is any left I just sprinkle the rest around the rest of the yard. It takes about two weeks, but the cats quickly learn that if they go in your yard they are going to experience pain in their resperatory system, and when they lick their little paws, they experience a new level of heat in their mouth. This causes no harm to the cat other than what you feel when you eat a pepper. No more cats in my yard.One more option is called Critter Ridder. It is available at most garden stores. I've seen it here at Lowes. It is about $20 for two lbs. of it. I have not used it though, the pepper works for me and it's cheeper.