Thanks Gents;
I can rent an excavator and raise the frog pond dam 3'. Maybe can scrape up enough soil to build a 4' berm around the shallow end. If I get lucky and can utilize a solid slab rock, I can dozer scrape the deep end then hand shovel clean off the initially soft sandstone. Fissuers can be packed with bentonite/kitty litter or possibly a liner can be placed.

However, has anyone put a liner in the deep and let the marginally clayey soil take care of the shallow sections? (Me thinks it can be done if one puts a load of 4" rock to hold it down and edges tucked at the 3-4' zone)

Self-educated rednecks, the real intelligentsia.