I am so sorry you have been going through this problem with your kitty for so many years. I completely understand your frustration, and commend you for sticking it out this long. From my perspective, I have a few questions for you:
1. How many litter boxes do you have in your home? Where are they placed? Are they closed/hooded or open to the air? Are the boxes high sided?
2. What kind of litter do you use?
3. Do you have other animals in your home with whom Mickey shares his living space?
4. Did the anti-anxiety medication prescribed by the veterinarians at Tufts actually help Mickey stop urinating/defecating outside his litter box? Can you tell me exactly what that medication was?
5. Has Mickey had a full medical workup done recently? In other words, has he had his bladder imaged for stones? Has anyone submitted a urine culture to rule out a UTI? Have you tried changing Mickey's diet to a prescription diet designed to deal with cats that have chronic cystitis issues?
6. Are there any feral cats that roam around outside your home?
I don't feel you are at the end of your rope with what can be attempted for Mickey, but again, I do understand how frustrated you must be at this point. If you're up for it, I would suggest making sure Mickey is evaluated fully to rule out medical causes that might make him urinate/defecate inappropriately. In the meantime, you may need to experiment with adding more litter boxes to your home (and experimenting with different types of litter boxes themselves), making sure you place them quiet areas of the home that are easy for him to access, and using litter that he likes to actually dig into (which usually takes trying all different types). Also, if Mickey shares his living space with other animals, I would consider isolating him to his own living space for a while, which would mean confining him to a bedroom or even a bathroom initially, before you attempt to "reintroduce" him to the rest of the house. If there is any possibility that feral cats are roaming around outside, try keeping Mickey away from doors or windows that would allow him to get close to their scent.
Judy, again, this problem is a very difficult problem to solve, but if you're willing to keep trying, you might be able to find the right living conditions for this little guy. Behavioral modification drugs can be helpful, but his environmental issues need to be addressed in great detail, because those drugs won't solve the problem 100% without environmental modifications (that I mentioned above).