I have dug over a lovely area at the bottom of the garden, all soft earth and a sprinkling of cat litter on top, one of my cats has got the idea but the others keep pooping on the grass! I scoop it up and deposit it in the dirt so it smells like a toilet over there, but they just keep going on the grass. We tried cutting the grass short, we tried letting it grow so long we almost lost the garden bench, but to no avail.
How on earth can I persuade them to stop going on the grass? 