Add cap blocks to the top row of a block or stone retaining wall. You can add a layer of masonry adhesive to hold them in place, then back fill. Or you can backfill as you go, then add the cap. Either way, it provides a nice finished look, much like edging added to a paver patio.
California Gold Gravel 2" and Wine Red Gravel 3/4"......The two important features of this photo are how to use different sizes & colors of gravel for contrast in the landscape. The use edging to separate different gravel materials in nearly every instance is a waste of money and don't look good or last very long. ...http://www.earthstonerock.com/Wine-Red-Landscape-Gravel-Prices-s/596.htm
On the left is Palomino Coral 5/8" and the right is Apache Brown 5/8". http://www.earthstonerock.com/Apache-Brown-Landscape-Gravel-Prices-s/585.htm http://www.earthstonerock.com/Palomino-Coral-For-Sale-Wholesale-Prices-s/1024.htm
High Style, Low Price This outdoor room looks expensive. but that's just what the homeowner wants you to think. Inexpensive building materials such as gravel, cinder blocks, and pressure-treated wood form the backbone of the design. Tile backboard and salvaged plywood, stained a soft blue and attached to a custom frame, give the tiny yard privacy.