I keep chickens, ducks and quail in the garden. My children love them and collect the eggs daily.
We had a plague of fox. They chewed through the wood and wire of the coups. They also dug under them. They regularly defecated on them as well. They clawed at them nightly, scaring the poor birds to death. Eventually they got in by breaking through one of the Perspex windows, killing a quail. They then started to turn up in the day trying to kill the birds.
I bought an WCS Collarum. It's basically like a giant mouse trap that throws a snare over the foxes head. It had second spring that fires just after the first. This spring whips the snare tight around the foxes neck.
The good thing about it, is that when it is buried, only the bait can be seen, as in the picture.
It's also canine specific and won't catch cats for example.
It's quite effective. I managed to catch 3 out of the 12 foxes in the garden with it. To be honest it failed on more foxes than it caught, despite trying to be meticulous in its set up. Once it failed on a particular fox and I moved the Collarum to a different location, the foxes would often scratch the ground to uncover it and leave it alone. But it does help remove some foxes, which saved me some trouble.
It also doesn't harm the foxes, if you don't want to kill them. I personally dispatched them.
After the foxes were removed, we didn't see a fox from April until September. Leaving the birds to roam freely around the garden, without the worry of losing them.
The Collarum in action: This is not my video.