What is the reasoning, though?
Is the air pump not strong enough?
Well I cant speak for anyone else but my pond is generally 3.5ft and even more in other places. A pump wouldnt be strong enough to keep a hole in the ice at that depth because by the time the aeration coming out of the stone reaches the water level the aeration spreads out too far and the water strength just isnt there. Aside from the water strength issue, I wouldnt keep it in on the pond floor because in my own opinion the muck or whatever is on the floor could end up clogging the stone.