Richard shows how to maintain a mini split; Mark and Jenn build a garden retaining wall. Richard Trethewey demonstrates how to maintain a mini split, showing how to properly clean the indoor and ...

Retaining walls vary in design, and can be made from concrete blocks, stone, brick, wood or even boulders. Some are built into a cut-slope or backfilled to create usable space behind.

So, if you're planning to build a 4-foot retaining wall, convert 4 feet to inches (4 times 12) to get 48 inches. Then, divide 48 inches by 8, and you'll arrive at a 6-inch depth.