Dave -
I second cage rearing some BG or seining off a section. If you feed the penned BG food they will grow quickly. They're pigs at feeders.
With respect to the concrete barrier - have you considered cinder blocks, rebar, and quickcrete? Maybe you won't like the look and I don't know the size of the wall, barrier or pond, but I've built some pretty big things using these three component and they weren't expensive. Just rent a mixer (I used a 5 gallon bucket with a stir stick and another bucket adding water...).
