Exactly. Good guess. The local pool builder would not even come to our house to look at the backyard and give us a bid. That should have been a clue but there is an inground gunite pool about 4 miles down the road from us so we never thought about ROCK. Closer to town and in town isn't as much of a problem. We just happen to be in an area that has a shallow soil layer. NOW I found out about that. The aerobic septic system swe have should have been another clue. No field lines and the treated water is attached to a sprinkler system.