Walls of Stone: How to Build Drystone Walls and Rock Fences: This project by the National Center for Preservation Technology and Training (NCPTT) produced a video for training technicians in correct methods for preserving stone walls and rock fences. The video is a primary training resource, providing graphic instruction on how to repair, rebuild and relocate stone walls and rock fences. In addition to providing training to practitioners, the video explains fence and wall construction to archeologists, engineers, preservationists and conservators.