Cats make a toilet in my flower box

I've had lots of cat problems and tried a lot of these methods. The only thing that seems to work is not to leave any bare earth exposed - not easy when gardening across the seasons! I did have an area that was covered in wood mulch when I lived in Grimsby, and they didn't seem to poo on that (until I turned it all over and there were some well rotted areas that probably looked like soil to them) so maybe applying plenty of uncomposted mulch (that your plants can grow through) might work. I suspect cats are going to be a perpetual problem in my gardening life, so I really hope something works!