Quote Originally Posted by DanMan View Post
We suspect a critter may be responsible for undermining the liner in that spot. The depression is about 4 1/2" in diameter and an inch and a half deep to two".
Sounds like you may have a mole, or three, or more. I'm not sure why, but this year we've had a bunch of questions about them. No feedback, so far, on how things worked out.

However it appears the only solution to moles involves killing them. Not sure what you think about that, but repeated excavations like that, under your pool could get to be serious problem.