Just finished building a elevated flower bed for a customer. Approached it the same was as before, but due to the slope of the yard ended up putting more layers than I like. The far edge is 2 high with one buried, and the end closest to the drive way is 6 high with two buried. Finished the job and thought I was done, well it rained that night, and now part of the wall have sank.... And the remained (the 6 stack high) side is unstable. Pressure from the dirt behind the wall (as this is a elevated flower bed) is pushing the high side outward and on the ground (falling over). Customer requested the bricks not to be mortared, as they might move them over time, but how do I resolve this stability issue. Yes I did "geo grid" them with each layer breaking the joining brick below and no two levels with the same brick line, if you are going to ask. Is there something I can use to stop this?