When I rebuilt the spillway, I also raised the pond about 3 feet. That's where the flooded timber you see in the picture came from.
That was a good move right there. Made the pond deeper, bigger, and added structure! Even the terrestrial plants on the shoreline you drowned will provide some cover for baitfish for a few months.
How are you going to install the rock? I suspect an old pond will have a fairly soft bottom. If you grabbed a load of your biggest rocks you might be able to create a bit of a slope "anchor" by dropping it straight down at the maximum design depth of your rockpile. For example, if you drop a load in 6' of water and then work your loads up the slope to your minimum design depth, that might(?) be stable on a moderately steep slope.
