If they take the clay from the pond bottom, plate over the top 2 feet of sand and compact it properly...
Absolutely. Since there doesn't seem to be any ground water issues, I'd make that pond as solid as a bathtub. Even with the evaporation, if it's solid, the pump should keep up with the water loss.
I've heard rumors that there's deer down there. Any truth to that?
![laugh laugh](/images/graemlins/default/laugh.gif)