Watermom's right (of course). If I we're attempting such an install, I'd dig a couple feet into the hill past necessary then dig a little trench all around where the ground's higher than the pool, line the trench and dug out face with landscape fabric and maybe install drain tile to divert the water away from the pool. Backfill with stone as the pool fills. Or maybe a retaining wall - more digging and hauling / lifting.
Good luck
P.S. Glad to hear you worked through your first year with the "Gateway" pool. I was hooked by a little donut that was $70 new at a toy store.