Cats shit on my freshly dug soil, for preference. I'm not prepared to remove it - I found the worst part of dog ownership was dealing with his turds, so I'm damned if I'm going to handle the ordure from other people's moggies. The worms, slugs and other natural processes seem to make it disappear. If it does leave potentially damaging toxins behind I don't know, but they haven't killed us yet, nor, so far as I know, made us ill.