Try the MN Waterfowl Assn site as they have plans for both wood duck and Mallrd hen nests.
It is too late for this season--but contact me this winter and I'd be glad to give you a few tips from my experince of installing and maintaining the 40+ I have up.
You may still want to plant good food in the water if there is not the right kind in your pond already. Try Wildlife Nurseries. You can always call them and they can recomend what would be best for your local area.