I have a great update on my mom's dog that was compulsively licking his back to the point that the hair fell out. He would only do this in his "in-in", his crate that she had used to crate-train him. So she noticed this and took it away; it had been an oversized "pet taxi" thing.
He has literally stopped compulsively chewing his back now. His hair grew back quickly and seeing him on my visit there yesterday, I was amazed. And he still has an area where he can retreat and call his own; she set up a doggie bed in a spare room and now he is more apt to curl up with his "sister", her other dog, there.