I definitely agree that re-training is something you could try before thinking about getting rid of him. Cats are very sensitive to changes (changes you might not even notice), and become territorial easily. Often cats pee/spray outside of the litter box if they are feeling threatened (for any weird reason), and a common solution to this is to have litter boxes without lids and to keep them in an open area, that way there's really no place to "mark". Obviously I don't know your whole story, so that might not apply at all, but I figured I would throw that out there just in case. Anyway, good luck, I hope things get better!