I don't think this tip has been entered before.
On my local farm there are several racks where the reds have been cutting through but i rarely bump into them, however in my experience they are creatures of habit.
They love our cover crops and the aniseed in the feeders.
I set up an alarm clock (get 2 at poundland) with a length of fishing line across the rack, make sure it is at a height so that a fox or badger can't set it off.The line is attached around the battery and the clock stops when the deer run through,simple.
However you don't know whether its am or pm so you do need to check both ends of the day, it does work,honestly!
saw this done on one off the warrener films, he did this to find out what time the fox visited his baited area