I politely disagree. I think a diffuser run by a small compressor in the center of the pond would indeed keep a good size hole open as a refuge for the ducks. Especially as far south as Missouri. Wouldn't have to be a large compresor.

I would call the folks at Stoney Creek in Michigan and they can give you good advice as well as sell you a very small compressor, airline, and stone to do the job. You should be able to get by with one of their smallest compressors.

http://www.stoneycreekequip.com/form/air_compressor.htm

The Gast DC 22 would be plenty for your small pond.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.