Hi, Im looking for ways to prevent this from happening when I fix this damage. 2 yrs ago above ground pool was installed, it has been perfect. We just noticed a lot of little rusty bubbles on the outside of the wall, started to do some paint repair. We already know that we will be pulling back the liner to see the wall.I never expected my 50 yrs warranty pool would have this problem after just 2 years. There is also a lot of sand and water trapped between the wall and liner, you can feel it. When you swipe up the pool wall, it looks like mud coming out of little holes on the out side. I cant find any holes in the liner yet, there are some sharp feeling bumps. We also have 4-5 good sized divets on bottom, and one right on the cove. The pool was put on a sand base. Its on a slight incline, but its flat and was dug out. We have retainer walls with french drains around the high end. we us a pentair intellichlor SWG, that works so good, now I may stop using because of all the rust starting. Oh, BTW, the pool manufacturer is Swim n Play -went out of BZ, and the pool store owner would not even speak to us, and suggested it looked like fertilizer damage, well I dont use fertilizer. So, I am on my own. Any advise helpful.