Drake Maiden.... just so ya know, a weasel CAN climb trees and are also good swimmers. Looks like a moat around your ducks is out of the question also.
Maybe a motion sensor owl? They have the ones whose eyes glow and they hoot whenever there is movement and the ducks shouldn't be moving much after they bed down. Just a thought.
A good dog is valuable for this...wish I could loan you my Jake...he would eat your weasel in one gulp!
I have a cat that can handle weasles. She is not very big. I think she weighs about 6 pounds, but boy she is a good hunter. Her name is MaCat. She adopted us and has lived on my front porch since last summer. We were going to rehome her after she had kittens on my front porch this spring, that was until she started bring us mice that she had caught. After taking her kittens and having her fixed, she went into over drive on the hunting. Along with a half dozen mice almost every day on my front porch, she caught 4 weasles. Three had bodies that were about 8 inches long plus their tail but one had a body that was about a foot long plus the tail When I saw her trying to carry that one across the yard, the best she could was drag it 5 or 6 feet then drop it and get a better grip on it and drag it some more! She has a sweet disposition with us but I wouldnt want to be a mouse or weasle!
My favorite barn cat was a female cat too. She was worth her weight in gold. When I moved up here everyone back at the stables fought over her. She was adopted as a ferral cat and was pregos...had her kittens, go fixed and hauled giant rats from one end of the runway to the other.
We had a weasel problem a few years back. I took the pee thing to the next degree. I used my own! Collected in an old coffee can and poured all around the chicken pen!
It was very late in the game so I am not sure how well it actually worked.
They also say dog hair or feces will deter weasels. I know dog hair amongst my greens in the garden seems to help a lot with the rabbits.