I am one of those people who ultimately didn't lock up the chickens at night. I started out doing so for several months (we had two), but they started getting impatient at 6am so I connected a string from our bedroom window (second floor) to the door to their run, left the latch unlocked, and just pulled it open as soon as they started up. Then I figured I'd just leave it open. In three years we've never lost a chicken, rabbit, or duck to a predator, but we live in a neighborhood and seldom see any of the listed predators. Ironically, yesterday I was sitting looking at our ducklings when a shadow passed over, I looked up and saw a very large hawk fly over our house. It seemd to be heading somewhere rather than scouring the ground for food, but I thought it was interesting nonetheless. FWIW, we lock our mama and baby ducklings up every night, but dad stays out (because he's not a nice dad.....or partner).
I would definitely do everything I could to keep the ducklings safe, but I am one of those people that feels that a certain amount of freedom for the animals is a healthy thing. I try not to be stupid about it, but one bunny has been free-ranging (so to speak) for a couple of years, our chickens did so as well, and our adult ducks do (other than with the babies, which we try to supervise when they are out). Hopefully you'll find a set up that works.
-Dave