Ric,

What you say makes sense to me, kind of. Seems like it would saturate whether it was seeping on through or not, but then just about all ponds seep some. I just don't know. Seems that theoretically, there is some amount of clay that packed from behind would hold....whether that is 1 foot or 15 feet I don't know, but given enough clay it should hold, seems intuitively...but intuition doesn't work on ponds.

Any other opinions?

I guess time will tell and I'll try to pack as much as I can back there...I've already added about 5 feet of good solid clay to that location...and made a big hole for fish on the front side.