In my area we get about 3.5 seasons hot enough to swim and I have a limited budget. What I have been doing is setting up an inflatable ring pool (14' x 3.5') to cool off in. The problem is my yard has a slope. My strategy is good I think. I place a board in the middle on a 2.5' bolt and try to work around with a level, digging the high areas and building the low areas and adding lots of play sand. See the images for examples.
My problem is the far side (where the wall is) always compresses and the pool leans as you can see in the third image. I am constantly afraid a kid will kick against that wall after the water is high and the whole thing will just roll down the hill.
What should I do that could solve this issue for less than $100?