The root structures of trees and other foliage is mother nature's best retaining wall. A civil engineer can design structural reinforcement to sustain mud slides but it's a very complicated project and one that would probably only be looked at if you were in an area of very high risk. I want a new TV but am afarid to invest. When you get into the larger sized TVs, tube technology is compromised. That's why you'll see projection systems supporting the larger screens.
Sound insulation is a specialized area of home construction.
Owens Corning company makes several sound insulation products. Generally speaking, insulation does offer some sound proofing qualities. But materials specifically designed to reduce sound are more effective. Two things come to mind. Number one, the least expensive solar energy is passive energy.