You should consider making a duck pen like this:
http://welbars.com/lib/exe/fetch.php?media=ducks:bantam_duck_pen.pdf
I have 3 of them now and they are working really well. Easy to clean (and longer between cleanings), no mud, swimming pool that they really enjoy, cleaner eggs, up high so they birds seem less skittish to me, perfect predator protection . . .
The only problem is they are best suited for lightweight ducks, because the wire floors are hard on the feet of heavy breeds. I have only kept bantams in these, but I think they would work for the lightweight layer breeds also, esp if you looked for sturdy, coated wire.
Of course, I love my bantam breeds - Australian Spotted and Miniature Silver Appleyards.