I am assuming that the pond is in Missouri vs. Mass or OR. I was going to suggest a diffuser in 3' of water for winter aeration, but if the pond doesn't get iced over for any length of time it isn't necessary.

www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).