I'm not an expert, but I know that before 1997, the program in force at the time allowed people to cut a key into the base of the cliff before introducing enormous rocks into the opening. After that they would pile up stones under a particular angle. As you can see in the photographs I showed earlier, it was done with concrete walls at the time. In one of the photographs, the wall dates back to the late 1950s.
Expertise is essential. Every case is different and the solution or approach may also be different. Sound expertise is therefore required in this area if something is to be built to last for the long term, but perhaps not necessarily permanently.