Sometimes its about impossible to get them to stop because they have done it all their lives and its now a very well ingrained habit and addiction. Even if whatever initially caused it (bordem, ulcers, stalled all the time, stress, etc) is no longer an issue in their life.
We had a cribber here and in his past he even had the cribbing surgery which cuts tendons in the neck so he's not supposed to be able to crib. Well he found a way around that by using different neck muscles! Thankfully his windsucking noise wasn't as loud as normal due to the surgery but he was still doing it. Cribbing collars did not work. My next step if I kept him would have been a cribbing muzzle - they are light weight wire baskets that go around the muzzle. Much more open than a grazing muzzle but prevents the horse from getting its teeth on items.
Another thing is put hotwire up. Some horses LIKE the taste of peppers and such - so you can't count on those as a deterrent. But most don't like a shock from hotwire.
Unfortunately we had one of our younger horses picking up cribbing-like habits from that horse. No windsucking but started putting his teeth on everything trying to immitate him and ended up more chewing type behavior. Thankfully consistantly correcting him on it has led to a reduction and seems like the behavior isn't really sticking, but we have to stay vigilant.