Where is the spot that he keeps peeing? Can you either make it less attractive for him to pee there (like by putting tinfoil or some of that vinyl carpet protector stuff with the nubby side up), or maybe place a litter box there and very gradually move it to where you want it?
When was his last urinalysis? Do you have a copy of the results?
Have you tried Dr. Elsey's Cat Attract litter?
And lastly, what does he eat?
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler