Have you had him checked for Feline Diabetes or Hyper Thyroid? both of those may cause them to not use the litterbos. JAT
I was thinking the same thing as I read through the thread.
My daughter's cat started peeing everywhere. Being diabetic myself, I started becoming suspicious of his behavior and demeanor, and suggested the diabetes possibility. She took him to the vet finally, and sure enough, it was diabetes. He gets insulin now (and a better diet), and is much better...