Tips to stop cats pooping on my lawn...seriously...MAD here?

Actually I believe that you can purchase a spay at pet stores, it will help 'animals to leave it alone'. Also, maybe you could put a litter box outside. Its never to late to teach them to use it. I know that it rains a lot, but spray the lawn as often as possible, & put a couple of litter boxes outside. You never know, & its worth a try.