Tater the Great Urinator

This problem is not getting any better.  We moved him into the garage where he stopped using his frequently cleaned litter box and started going everywhere. He also pulled several keys off the laptop that controls the mill.  We put him in a large dog enclosure in the garage with his litter box.  When I let him out and hold him, he is his friendly purring self.  But it is now very cold in the garage, so we moved him into the laundry room a week ago.  Again, his litter box was kept very clean.  The smell became a problem because he was spraying the tarp on the outside of his cage.  We have moved him back to the garage, with an electric heater aimed at his enclosure. 

I feel bad for him, but we have run out of solutions: wet food not dry; away from the dog; our vet has examined him for the common illnesses and found him healthy; there are no other cats inside or outside (outside cats are coyote chow).  I would feel really monstrous putting him down over this.   If someone in town was willing to adopt him as an outdoor cat, and feed him regularly, this would solve the problem.  He is a very loving kitty and he is now 16 1/2.  He probably will pass in the next couple of years at most.  Does anyone have another solution?