Unfortunately, my boy ended up having quite a few issues and he's passed away. His last days though, I faced the door of the litter box towards the wall and hung a puppy pad on the wall and had another one on the floor between the box and the wall.
That's my mastiff/great Dane mix with Harpo, my Rex, and Maeby, my little black kitty. I also have other rexes, a Rottweiler/lab, 7 hens, and 3 tarantulas.