trapsht,
I am in the same situation right now, i overstocked my 2 acre pond b/f finding pond boss so im doubling the size of it to fix the problem. At 5 or 6 feet we have water starting to seep through, it will add approx. 1 foot of water overnight. What im doing is digging various deep sections which will hold the majority of water. Doing it this way makes for a ton of structure, cliffs, craters, ledges and deep spots. I'm digging in pure clay, so the shape stays for the most part, a little will wash over time but you will always have something different for the fish. Just my solution, may not work for everyone. It looks like I have several sections in the bottom of my pond with levees seperating them, but it allows me to work with dry dirt at the same time. Slope it to the deep spots so the water will drain to it.