Six of us clubbed together and builta coop and run around 6 weeks ago, and have added to this just this week, for the 7 new chickens(16 in total).
Foxes are endemic in quasi-urban Surrey, and we have seen them sitting on top of sheds and now the wire covered runs.
I am surprised at the number of times I hear of chickens being taken by Mr Fox, that some of us don't cover over the runs with plastic coated wire or similar, like we have done.
We are paranoid about losing our chickens, so the coops and runs are a bit like Fort Knox.
Foxes seem to be able to leap up at least 6 or maybe 7 feet with ease, and when they get into a run/coop they will slaughter all available chickens before starting to think of eating one!