Where ever you put one it will have to be predator proof even on an island in the middle of a pond or you'll be heart broken one day.
Mine although I have 13 Muscovies, but the point being it needs to be secure. Ducks on the left chickens on the right
Mine are all in the same house but there is a wall and door dividing the 2. All they need is something strudy with lots of ventilation be it windows or cut outs with hardware screen to cover, we have windows bought from habitat for humanity's thrift store with hardware screen covering the outside. easy to clean. some folks have used the dog house from Lowes for a few it has a roof the opens for easy cleaning.
Doesnt have to be anything fancy Just a 3x3 foot box that is wind proof and dry. Make it easy to clean out though, a hinged roof or front panel with a smaller door for the ducks. Being you are from Oklahoma tornado proof would be a plus.
I think your only problem is going to be making your duck house as secure as you can, using hardware cloth on all openings and having a secure lock on thier door for night. plenty of ventilation for moisture to escape and for good breathing. No one thinks they have preds until they get ducks/chickens or geese then they find out. Best to do it right the first time then no heartbreak. another thing you need to take in to mind is the threat from under water, snappers have been know to eat ducklings and also severely maime adult ducks so before putting them on the water you may want to check and make sure your pond isn't harboring snappers there are other threats too, sliders I have heard can cause injury and also some types of fish. Make sure whatever you build isn't easily dragged into the pond either.
