By stuff, do you mean wood or anything they can reach and get their mouths around?
How often are they worked or at least let out of their stalls? Sometimes it's boredom. Sometimes it's a learned behavior caused by imitating a wood chewer (not to be confused with a cribber which is another awful habit).
It's a really difficult habit to control once it becomes ingrained.
Well he chewed his hay pin ohh the wall and 2 boards off his stall. When they stayed in there stalls for a week cause the fence got messed up. Now if we leave him in stall over night he chews on all the wood
It sounds like it started out of boredom and is becoming a habit. I would coat everything possible with soap, motor oil, cyan pepper, or anything distasteful (but not harmful) for a while and be sure to give him plenty of hay.
Another useful thing is a stall toy. What you need to do is to give him something to occupy himself.
I think this would be out of boredom, my paint does this on the posts in his pen but it could also be a lack of vitamins and such hence why some horses chew trees? Is he getting everything he needs to cause this or is it boredom?
Boredom (or more likely the fact that horses are geared to graze 14+ hours a day) can be a cause, as well as stress at being locked away from pasture mates, lack of forage, gastric ulcers etc.
Unless there is a very good reason to stall this horse, it would be a good idea to just leave him out at night. If he can't be left out at night then a grazing muzzle would be a good idea while he's in the stall to physically prevent him from chewing on things. And be sure to provide plenty of hay while he's stalled---preferrably in several areas in his stall to give him a little stimulation by requiring that he move around and look for it.