I continue to be amazed at how retaining walls are spec'd out in modern day landscaping. On my drives I go out of my way to get out of the car and get up close and examine modern retaining walls. Often they are built out of a concrete product and very often are falling forward. I think it's understandable when their spec's are compared to even a really rudimentary dry stone wall that will last centuries. Mass retains mass, and all other "cheats" are doomed to fail. I've had these discussions far too often with landscapers, designers and landscape architects.... the proof is in their lifespan which can be witnessed by simply going through a google search on european retaining walls. Even the poorly built ones there will outlive the modern versions here.... Dry stone construction is the ultimate manner in which to build a retaining wall.... the difficulty is that it comes down to the skill of the builder which varies tremendously. This is the reason that certification schemes like that laid out by the Dry Stone Walling Association of Great Britain are so important. I would greatly encourage any young waller to seek out the scheme and to train with as many master craftsmen as possible to gain experience.