We
We use plastic storage totes. You just cut a hole in one end for the ducks to come in and out of. Our ducks are all free range as well.
I'll post some pictures of our nest boxes..
thanks I would like to keep my ducks free but just don't know about the neighbors dogs as I had a bad experience with chickens and turkey but I have a door on the fence so I think I will let them lose I will send you pics to later