I think that is why they are staying on the ice, they still have acess to the water and they feel safe there. They are in the middle of the pond and won’t even come near the edge. Only thing I can think of to do, is call the fire department. Not sure how that would go?
How wide across is the pond? If it's not too wide, you could take a long piece of netting, stretch it across the pond with a person holding each end, and then they walk it across the pond and herd the ducks off with it.