My parents have an old retaining wall (30+ years?) that needs to be replaced. They are open to any kind of materials, it doesn't need to be wood. What is the easiest way to build a new retaining wall that lasts about as well as this old one? It is about 4.5 feet high and 18 feet long. No problems over the years. Most of the plans I have found online (like this http://www.mrgrow.com/Tips/98/tip04.htm ) are for new walls, and seem to involve a TON of digging. I'd also consider regrading this if it makes sense.