My TB is a serious ulcer type too. I’m sure he had terrible ulcers on the track and then for several years of showing with me. Treating those ulcers is something I’ve posted about a ton, so I won’t go into that, but we settled on a routine that has kept him in great shape for the last 6 or 7 years.
But he is just plain terrible about the girth. Like you, I think it’s a learned behavior and the time that he gets away with acting like a jerk. I’ve had him for 13 years now and nothing I’ve ever done has made the slightest difference, and I’m convinced that nothing ever will. Every single day he tries to step on my foot while I attach the girth (doesn’t make a difference if I hook it on the lowest holes and it’s not even really touching him or tighten it from the get go). So every single day I poke him in the shoulder as he tries to stomp on my foot and do it until he puts his foot down and stands. I tighten it to where it goes on the one side and he pins his ears and bites at the air. Then I go to the other side and he’s pretty much done with acting up. I tighten the other side (the side that actually makes it snug) and he does nothing, and then yawns a few times after I do it.
I have a mare that’s a little bit the same. I think she was ridden in a TERRIBLY fitting saddle for a couple of years and had a lot of back issues when she came to me. She’s always been a drama queen about the saddle too. She’s 23 this year and has been with me for 15 or 16 years.
I was starting to think that maybe I just teach my horses to be bad about saddles. But in the last decade or so I have had a string of youngsters that I’ve started and developed (and had for anywhere from 1 to 7 years), and none of them have had any issues with the girth at all. I do have one that’s a super ulcery mare who was a little wicked about girthing up when I got her. But I started feeding her a treat before I tighten the girth and then a treat after, and now she totally ignores the girth and is just focused on sweetly asking for the treat.
I’m sure none of that is particularly helpful, but I can say that I empathize with you!