Good info from all, thanks so much. The frost heave issue concerns me.
We're 8 miles out in the country on 6 acres (should have said that)
with no real access to our property, and there are lots of things more
dangerous than a pool should someone decide to come onto the property
and mess around (they'd have to make a very hard effort.) No zoning
codes apply out here for the digging, or the pool. Taxation is likely
an issue, but as I understand it, if it's 12" out of the ground
(partially buried) it's not a big deal.

Some good things to consider though. I do like the idea of a deck, just
might need to do some more figuring on the materials cost. I'd do all
of the work myself. AND, when the kids move out, I don't have a big
hole in the ground (well, other than my pond.)

Interesting about the membrane though, the soil here is like carving a
statue, when we dug the hole for our house, it was like brick on the
sides of the hole.

Keep the ideas coming!