Gosh, I'm sorry to hear about these problems with Minion. I am in the same boat. Our cat Scooter will pee all over the house if left to his own devices, and it's going on 10 years now!
We tried everything too, and nothing works. I have to agree with it being a declaw issue. Scooter is also declawed, and I really believe his peeing issue is a result of the declaw.

Scooter is my husband's cat, and he just loves that cat to pieces. The only solution we've found that works (most of the time), is to keep Scooter caged during the day when nobody is home to watch him. The cage forces him to use his litter box, and he has shelves to lay on, and his food and water are in there also. Sure, it's an eyesore taking up a huge chunk of our kitchen, but it does give us piece of mind that Scooter isn't peeing all over the house while we're gone.

It's not a very good picture, but you can kind of see Scooter's cage in this picture:


For the longest time, we felt so bad about shutting him in this cage, and I even asked my vet about it. Considering cats sleep 18+ hours a day, the vet said that it's not harming him at all keeping him in there when we can't watch him. Even when we open the cage door to let him out after work, he sometimes just opts to hang out in his cage (just like he is in this picture). It's his safe haven, which is a good thing.

Perhaps this is something you could try? Take it from someone who's had a peeing cat for 10 years!

**hugs**