I come from the countryside, I'm incubating duck eggs but have 5 13 week chickens.
We killed most of our large predators in England long, long ago, but the foxes are pretty starving, desperate animals.
I buil a massive enclosure a few months ago; 25ft long, 6ft high and 8ft wide. I also dug the wire in over 1ft into the soil, with a 1.5ft skirting inwards.
Build an enclosure like you're protecting them against a desperate hungry person. Don't underestimate the thought process of a predator who is a natural problem solver.
Create awkward and sharp edges at weak points, such as where 2 lengths of wire are connected together.
Electric fences don't put off animals if they're starving, the learn that a sharp zap and then they're in, is totally worth it, unless it's REALLY high voltage.