couple more things -
DuckPlayer mentioned the trolling motor idea - I have SLAIN ducks using a similar setup. If you don't have a power source, use a battery. We had the ability to carry a car battery to the blind, and were able to run this thing all day. We broke ice, clamp the trolling motor to a 2x6 driven deep into the mud. We had a goose shell, with styrofoam "fitted" to the trolling motor and wired onto it, hiding the motor and post, at a bit of a funny angle, but nothing that seemed to scare any ducks. The motor, at it's angle, kicked water up OVER the ice, slowly opening a larger hole in the ice, AND more importantly, creating the perception of open water as the water rolled over the top of the ice. It was like magic...
Second, Yellowlab hit it - if you hunt the same ponds often, be SURE, like any place, that you give 'em time to rest. We try not to hunt the same ponds all week long. Maybe hit'em on a weekend, then hit the public marshes during the week, maybe hit the same pond on a Wed/Thurs... a nice rotation keeps the feathers feeling safe. I also realize that not everyone has the luxory of multiple opportunities to rotate around on, but my point is - give them a rest. I found it to be worth it. You CAN shoot off permanently if you try!