Live traps (box traps) are useless for foxes. You'd have to catch one by hand and stuff him in there to get a fox in a box trap. Old time trappers, using steel leg hold traps, can get them regularly. A few years back an experienced trapper caught 28 in one season at the farm. All with steel traps. I believe as he trapped the resident ones, others moved into the prime territory and were caught. That speaks to the skill of the trapper that he could get that many, and to the size of the unseen fox population.Good luck on trapping. Over the years we have tried several traps during different seasons for foxes. So far we've caught raccoons and possums and even the rooster once (He was released.) but NO foxes. And we've used every kind of bait we can think of. Because the chickens live in Fort Knox, I don't worry about the possums and raccoons.
The minute there is the slightest chink in the armor, the fox will find it.
If anyone has any sure fire ideas or even any kind of an idea, I would like to know it.
My plan is to never expose a bird I value to predators. It take a lot of work and money to build coop that way, but it's worth it. I would be happy to give advice to anyone about predator-proofing, just send (or post) a bunch of pics of your coop(s).