The only answer as far as I can see to foxes is electric fencing - get an energiser, connect up to hotstock. It does not kill them but like putting your hand in the fire you dont do it twice - hit the electric fence. Apart from a shot gun which one can only use with a licence and one is only going to get that if you live on a farm, but even then a farmer needs an electric fence as you cant watch hens every second in the garden.
Beware of chicken runs - Chicken wire is to keep chicken in - not predators out. One needs strong welded mesh, and wooden posts heavily weighted to the ground. Dont forget to have a solid roof on. Even then the hens may not be 100% protected.
So many people have lost chokes to them, as they are oportunised. They become desperate for food. I know I had one in the garden today, cause of the foot prints on the snow.
I believe a fox can jump high fences, but has to touch the top of the fence - which could be a disadvantage, with spikes on top. But there again one cant protect one's who garden or field.
Many anti-fox people, want their pet rabbit, cat, or hen ripped apart by a fox, then they might have a change of attitude towards the fox.
Remember - like burgulars dont give them the smallest opportunity, because foxes will surely take it.