Finding a hole in liner

[GraceByDesign]

Children tracking dirt in on their feet?
Children playing in dirt/sandbox and throwing dirt/sand which then gets carried by wind?
The Dog? (yeah, always blame the dog! )
Uninvited animals cooling off/getting a drink at night?

[treyk]

I would also be thinking along the lines of Grace. We have ducks and seagulls in our area. The ducks often like to take a swim in local pools.