Sympathies from a fellow cribber from hell (he has since passed on, God rest his soul, last year at the age of 24).
Metal angle iron may sound harsh, but my cribber actually had good teeth despite cribbing on metal. They only need to use enough pressure to create the air sucking, and he actually cribbed lighter on the metal than on wood. I would try putting some on the surface of his stall and see how it goes.
Consider trying Chaste Tree Berry. It is a dopamine agonist that works on the same (dopamine) pathway that is activated by the cribbing horse. This did reduce the cribbing desire for my horse. Your mileage may vary but it’s cheap. I got mine from herbalcom.com. I don’t know if they’re still in business because it’s been a few years, but I bought the whole berries and ground them in a coffee grinder. I think I used 2 tablespoons morning and night. I did 3 weeks on and one week off. Because it’s a dopamine agonist it’s good to cycle and then taper.
Ulcer treatment with Ulcergaurd made mine worse. Although I can’t prove it with certainty, I am convinced that the omeprazole caused delayed gastric emptying and resulted in IBD-like symptoms in the hindgut. I decided to use fenugreek instead (again, I used whole seeds from herbalcom, ground in a coffee grinder). Here’s a couple links to some abstracts. I can’t say for certain that it worked because I didn’t have him scoped again, but I was very satisfied by the improvement in his body condition and behavior. Very very cheap.
http://www.ivsajournals.com/article_4590_8.html
https://www.sciencedirect.com/science/article/pii/S0378874102001174
I found over the 16+ years that I owned him, the thing that affected his cribbing the most was herd dynamics. He was the alpha, but was really too nervous and anxious to carry that role well. He always did best with very docile horses who never challenged him. I always thought that maybe it was pain-related, but I had him through many episodes of injuries and stall rests, and it never affected the cribbing nearly as much as changes in herd dynamics.
Finally, I’m sure that you know the difference between cribbing and wood chewing, but his attacking the run-in like a beaver sounds like he may be a chewer and a cribber (God help you if so!). I would either start him on a high quality chelated mineral supplement, and possibly consider pulling blood to check his vitamin e and selenium levels. Stress depletes selenium, which can also affect iodine and other minerals in a chain reaction. Some nutritional tweaking might be in order especially if he’s already not looking up to par.
Good luck!