My dog Pip chewed the walls when he was a puppy. He left holes in the drywall while laying in the hallway waiting for us to arrive home from work. Large holes. Triple fist holes.
At first, since the hole was so close to the floor, we thought that maybe a mouse or squirrel had gotten into the wall someway and the Doxie that I had at the time was trying to hunt it down, but we finally caught Pip at it. He had rawhides, toys and chews, plus the doggie door for easy outside access, but apparently nothing worked for the waiting except gnawing on sheetrock.