I agree allowing horses on the AT in the GSMNP is largely to blame for the erosion on that section of the AT. Unfortunately, I doubt there is a way to fix this problem. The trails aren't going to be made off limits to horses (too many deep pockets among equestrians contributing to the GSMNP for that to happen) and the ATC / ALDHA have expressed zero interest in relocating the trail to less used corridor in the area.