The fox comes right near our pigs, at one point leaving dung closer and closer to them as if to challenge them, so I agree with pigs not being a sufficient deterrent, and foxes are so well known to chew through chicken wire that we never even risked it. It's heaving with foxes here: we recorded footage of them on 7 different occasions during just 1 night, of 3 different foxes. Plus we're in the greenbelt so no solid buildings or concrete floors allowed, the ground is uneven, and we had problems with the electric fencing used for the pigs before we started keeping chickens (both people and weather problems). And like Chris says, the electrics only need to be off once and you've had it. Just one person not hooking it up, a load of snow or a branch on the wire and it's no good anymore.
So for the chickens we used heras panels from the start and never had a problem, despite some of our neighbours losing many birds even in broad daylight. I strongly recommend using those panels. We didn't dig them in, we just put a very strong mesh skirt around it of about 50cm and tied it into the panels. We made a door in the mesh of one panel and this door has 2 bolts and a padlock (foxes can work latches). It was so easy and quick to set up and doesn't rot. Painted green it blends in beautifully. The biggest run is about 50m2, and it's a great plus that the run is high enough for us to walk around it - we're both 6ft2!