Cats in my flowers.....

I have 4 cats that are outside kitties, and two of them, brother and sister, keep using this one area for their toilet, and it's going to end up killing my plants. I have pinecones all over, but they just push them aside, and do their business anyways. What have y'all used to keep your pets from doing their business in your flower beds? I've heard of ppl putting down chicken wire, or something along those lines, and they say it works. I'd like to know what others' have tried, and what DOES work. Thanks so much.