Sarah - We used to have that problem in Fremont. I think about 6 cats used my front flower bed for a toilet. I tried everything--red pepper, black pepper, stuff from the hardware store they said would work. Nothing worked. My husband decided to try to capture the culprit and he did it. But after a while the cats got wise to the traps and stayed away. I don't know what else to suggest--Maybe one of those water spray things that have a motion sensor. Whenever an animal comes around and triggers the sensor, it starts to shoot off water like a sprinkler. And, cats don't like water.
What's a mother to do????
"Anything Chocolate"...that is all!