Bill Stock wrote:
The original pond had a shelf for the lilies, but I had to dig out the shelf
to make a shaft for my bottom drain shutoff. My original thought was to put
a plastic tote on the bottom to form an artificial shelf, but the surface
area of the bottom is fairly small. By the time I add enough slope to the
bottom for a drain, stabilizing a tote could be problematic. I don't think I
can rebuild a shelf out of dirt, as I don't have enough room to slope the
sides.

You might borrow the idea of sandbags under the liner. These can stack
and still be on a slope.

Chip