My 20 year old gelding will only wear a blanket when the temps drop below 30F. He will skinny out of blankets or sheets in warmer weather.
He does have a stronger appreciation for his blanket after sending a few nights sans blanket. Not done too be mean - the last night he did not have a blanket, it was in the high 30’s at the last check (around midnight) and the temps dropped into the mid-20’s by morning.
Knew 2 geldings (TB full-brothers) who trashed multiple blankets. They were trying to tell us they didn’t need them.
Like some people are comfortable in short sleeves with maybe a sweater all winter.
Agree with other posters, allow him to do without the blanket for a day and/or night to see how he handles it.
The Baker fly sheet over top worked when one of my horses was destroying the others blanket. It might help if he’s going after his own.
Buy a bottle of the original formula skin so soft. Cut it with water, about 50/50.
spray it on the outside of the blanket.
Horses do not like to taste that stinky stuff.
I have a tb who would use his teeth to rip the rug from the chest back.
I bought a shade cloth rug. I put that on him and sewed it with quadruple dental floss every single morning and put it back on. With the shade cloth rugs the material is stronger than the thread.
In the end I won. He now wears other rugs with no problem. I feel like I won. 
The blanket may be irritating your horse’s chest. We have one horse who HATES the Rambo-style clips that do up in one spot. It puts a lot of pressure on his chest and he rips at the clips until the blanket straps are done, and then slides out. He needs his blanket to fit exactly or he will destroy it. The same could be said for a blanket that slides back too far on the wither, or squishes the shoulders.
Maybe try a size up or something of a different style. Some horses are just really itchy and can’t handle being covered. Make sure he isn’t too warm also. My horse LOVES blankets and the one time I couldn’t get up to take off a layer when it warmed up, he took it off himself! Mind you, he didn’t break a single thread (I’m telling you, this horse loves blankets!):lol:
Trial and error! We’ve currently got our “blanket shredder” in two layers of blankets since it’s -32 with the windchill and he’s happy as a clam.
Another thing that can irritate some horses is the little ‘sizing tags’ on the inside of the front.
I do blanket repairs and after fixing the fronts of a couple of blankets for one particular horse, I decided to sew those stupid little tags down flat and he quit trying to rip the blanket off.
What about a free to eat muzzle? Keep him from destroying the blankets but not keep him from eating/drinking.
BTW I use grazing muzzles on my horses, so TO with muzzles are not a big deal for me.
Had one that would remove however many layers he needed to until he was comfy. Fully clipped in Ontario, he wore a heavy sheet all winter. Nut! Maybe yours is trying to do the same but hasn’t yet figured out how to grab the ass end and yank it forwards enough to step out of and ends up shredding them in frustration?
Mare at current barn destroys her friends clothes. She goes out alone now.
Fwiw, my own mare is the happiest she’s ever been in her full neck Bucas that she got new this year. I don’t have to ask her to put her head down to get dressed, she shoves her head into it almost before I’ve got it lined up with her head. (I’m a lazy blanketer and never undo chest closures)
Question - why would you not be allowed to use a bib for turnout? Is your BO/BM going to take the stress out of blanket replacement by doing it for you, or let you try a bib? If I were the BO/BM I’d be working a lot harder to help you find a solution.
I have one like this…he has gone through probably 30 blankets over the last few years until I finally got the plastic bib others here have described. Works like a charm and he doesn’t mind wearing it at all.
