Is it possible to cover your run? Since I've put up my netting, I haven't lost any more ducks. If that's not possible, putting up predator tape (a reflective tape that's said to ward off predatory birds) or even putting fake predators in the run helps. I have a huge fake dog in my run that may or may not be helping, but I haven't had any more problems with predators.
I have about 50 birds; chickens, ducks, turkeys etc. They free range on approx. 2 acres. We have issues with hawks and one very big bald eagle. I have lost a few chickens and one call duck. I haven't had a hawk take a bird; always just ripped them apart & left for me to find. I cant cover that much area so here is what I have done to help keep them away. I have hung about 30 old CD's on fish line from trees. All at different heights. Hawks don't like the reflections & the other birds, especially the turkeys, loves to play with them. I also found 1" red plastic ribbon/tape and basically decorated all my trees. Throwing the spool up over branches leaving 10-20' tails to blow in the wind. Hawks dislike the color & the movement. My husband says our backyard looks ridiculous but my birds are alive.