I tried all the soaps....didn't work. I tried tobasco and redhot...didn't work, they loved it. No Chew does work, but it wears off easily, you have to reapply alot. I put metal flashing on the spots they liked and that's the only thing that worked.
Note....mine are at pasture all day, have plenty of hay to last all day, have toys out the wazzoo and they still chewed.
also...I've heard some say that the horse who chews may be lacking some nutrient or something. I feed good feed plus give a supplement, one horse still liked to chew. It is just on one spot though. He can't chew it now because of the metal, but there are other places he could chew, but he doesn't....go figure