I have three very fine cats, who stay indoors, because so many of my neighbors have pit bulls. I have visitors on my front porch betimes. When I put down cayenne pepper they go away. You have to replace it every time it rains. But it's cheap and it DOES work. Buy it in bulk. I get mine from a Greek grocery store.

P.S. I'll take cats over pit bulls any day of the week and twice on Sundays.