Damon: I put in a windmill (Koender from Canadian Pond; see Sue Cruz' post above for link) last year and it kept an opening in my pond through this past winter. On some extremely cold and still nights (below -25C or -13F), the opening would ice over, but it disappeared quickly when wind started the aerator again. My aerator is ~6-8' below the surface though, and I would wonder if a 2' depth would give you sufficient spread of bubbles to keep much of an opening free of ice. (I posted a picture of my open hole in winter on another thread
here on this BBS.) Ducks enjoyed the opening during the early part of winter and other wildlife seemed happy to have access to fresh water during the coldest parts of winter.
