Moved about 8 wheel barrow loads of dirt out of the hole today. Almost all of the pond is at 30" or thereabouts now. I'm going to make a 6' x 14' frame out of 1/2" pvc to use to square up everything. I don't really want to put plywood against the walls. Maybe I'll get some thin press board, but I will probably skip it altogether. The 2x6 frame around the top with some inset 2x4s should be enough. I'm not really concerned about making this last a long time. I mostly want to demonstrate my liner folding technique in an actual build and have a pond to put fish in until November when it starts getting too cold to have tropicals outside. I plan to buy some juvenile koi to grow out or maybe some high fin banded loaches