wow! That;s nuts! You say that you have a dog yard.... is it possible to have a dog tend to the flock? I was sooooooo nervous when I got my ducks, because I have two dogs and I know how dogs are with small creatures. I have a crazy mutt - sort of like a hyena - slash - jack rabbit- slash - razor back pig - slash - Brillo pad things,... she is clearly part terrier (although I only assume she is actually a canine, haha)/ Terriers are notorious for having a very strong prey drive. Minnie, this dog I speak of, will actually chase down and catch squirrels. Therefore, I was ESPECIALLY worried about her with my ducks.
HOWEVER, both of my sweet doggies have surprised me.... Once they understood that "mommy" says ducks are not dog food, they have been AWESOME!
Ever since the 1st months or so of the ducks being outside to range, I ALWAYS leave one or both dogs outside with my ducks. The dogs will sleep generally around the same place as the ducks are and they all tend to hang out. I think it is because my dogs have figured out that the ducks are a good thing, because they all get to eat the ducks' food.

My dogs LOVE the ducks' food!
My point is that perhaps this is a good possibility for you... I have an English Shepperd mix who has been very gentle with the ducks... perhaps you have a dog who can be adapted to hanging out with your ducks too. I find myself feeling more secure knowing my dogs are around, because they will chase down and kill the deer, foxes, raccoons, etc.
I am SO SORRY about your drake!!!!!!!!!!!!!!!!!!!!!!