When I took on my allotment 3 years ago last October, I discovered a fox's den in the far corner. I left it undisturbed as long as possible, but having put my adjacent greenhouse up 12 months ago, they disappeared, and I needed to clear out the far corner as it was heavily laced with rubbish and brambles. Only half of the heap has been cleared so far, and looking at continuing, I have noticed paw prints and scratchings at the entrance to the den, so I presume it is still in use. I will have to proceed with caution, as I don't really want to disturb the foxes more than possible.