My name is Pico!

This is extremely hard. Pico is 6 years old, we got him when he was a kitten, and he is far and away the sweetest boy we've ever had. Although he is neutered, he does have an issue with spraying in our home
Due to problems with other house cats we have. We also had to fashion taller litter boxes out of storage bins from Walmart with the front cut out as a door. Most cats pee with their butts down, but Pico will stand & put his butt towards the wall and pee. This
Has solved the problem with him peeing over the walls of the litter boxes in the house but he still has issues with spraying. We've had two different vets confirm that there is nothing medically wrong with him, only that it's just a behavioral/territorial issue inside our home.
It's so difficult and heartbreaking to try everything in the book. Apparently most cats are brought back to shelters for this very reason. It would be best for him to be in a household with no other animals or small children. Thanks for your time