So now I’m leaning towards negative edge. Immediately after the negative edge would be the catch area comprised of a few aquablocks topped with appropriate sized gravel. Then followed by a rectangular reservoir that would be capped with a duck pen. The duck pen would be modular so sections could be removed if ever the need to get into the reservoir. Basically I’m envisioning building a deck over the reservoir with duck pen on top of the deck. So the reservoir would have no need for aquablocks or a gravel top, if all goes accordingly no one would know the reservoir is under the pen. Here is my next question: how shear and deep can I make the walls of the reservoir if there is only water in the reservoir applying pressure to the liner and the dirt behind the liner? I was thinking about maybe making a box of treated lumber for a structure for the reservoir and a foundation for the deck. If I could get to 5x10x4 that would be a 1500 gallon reservoir and that should be enough.