It all depends on the soil. The soil that I made the wall in has a lot of clay which compacts very nice. I did not install it by the book, because as you can tell money was an issue on this project. I did compact the soil as much as possible and added about 2-3 inches of stone dust. Any small walls I do like that I guaranty it for a life time. If it does ever sink at all it is not costing me much to go out there and fix my mistake, and it also helps sell the job.