Until last summer my cat was feral, at which time he adopted us and moved into my shop. When snow became deep, I provided him with a litter box in the covered lean-to where I store firewood and some machinery. That worked fine until the snow melted and Frank began spending time outside. One day, he came into the shop howling with his wet paws covered with cat litter. I decided it was time to remove the litter box and allow him to resume toileting in the woods as he had before he moved in. Now he is using the ground in the lean-to, which shouldn't be attractive to a cat for that purpose, as it is covered with a 3" layer of drain rock, i.e., rocks that are about 2" in diameter. How can I get Frank to stop using this area?
You moved too fast for him. Cats always follow strict routines, and your cat has designated that area as the "toilet area" so, following routine, your cat "toilets" there. You can't just move a cat's litter box. This confuses them greatly. First things first, you will have to put the litter box back where it was (the place he always "toilets".) Then every day, gradually move it closer to the spot you want it. Your cat knows (or should know) to go in the box to do his business. The trick is to move it not too far, but not so little that it takes you three months to get it to where you want it. Eventually, you will have the box (and the poo) right where you want it!
I almost forgot to mention, even with the slow move, if your cat persists in pooping outside the litter box or in areas he hasn't before, consult a vet. Pooping constantly outside the litter box can be an indicator of some pretty serious problems. Definitely try my suggestion before you jump to any conclusions about taking him to the vet, though, as most of the time, a medical problem is not the case, and you just made the move too fast.