Perhaps there isn't enough food for them in your area, my sister lives right in the middle of nowhere near the Mendips and she's never seen a fox, but there are no rabbits either. Maybe you could try putting some food down, that's the only way to attract them, try putting some raw eggs and some raw chicken wings ( not cooked ) down and if they disappear in a couple of days there are foxes around, I'm looking forward to seeing the cubs, I heard them last night but no sighting yet, last year we had 16 of them. Let me know if you see any.