So is there a level that the pond will not come up above?
If so (and bear in mind that I have zero pond building experience), might the potential leak be related to that elevation.
To rule out that possibility, could you stop any more inflow into the lake? Then see where it levels off at; also take into account evaporation and any rainfall.
So if you're loosing an inch a day due to evaporation (when theres no rainfall), but the pond is not loosing any more water than that, then it's holding water; thus meaning the leak is somewhere above that point????
