I just had the same size pool installed, the installer said to keep the warranty I have to backfill the pool up to 4", I said BULL. My last pool, a 24' round, rotted out after 12 years (a pool with a 35 yr warranty) which was backfilled with 3/4" stone. It seems grass clippings and debris finally impregnated the stone forming a stone / dirt. That seemed to hold moisture which probably helped rust it out. Also where there were upright supports which kept the backfill from rusting the exterior wall, it rusted from behind due to sand contact. I had them install this one with no sand touching the sidewall under the pool, I did this by using pool cove foam & putting a foam insulation on the pool walls. I also installed a liner pad. I haven't figured out what I will do on the outside yet. I installed drainage, pipe & stone around the pool (not touching it, but about 1 foot from base) to keep water away. I will probably put patio block against the lower "U" channel that the wall sits in packed with sand to keep any erosion from eating away at the foundation. I am thinking that I will spray the lower few inches with a heavy tar spray & attach heavy vinyl or something, then put large (ostrich egg sized) stone down. Anyone else have any suggestions?