I see from the pic, you have a fence of some kind around the coop.   A fox can go over a 6' foot fence, like it isn't even there.  And if the fence has a roof, and he can't get through it, they can darn near outdig a groundhog.  Some people go with a hardware clothe surrounding cage.  That can get expensive.  You could run a hotwire around the outside of the fence, about a foot off the ground.  Fox comes up, takes a sniff of the strange wire, and gets a 8000V snootful.  He won't come back for a second try.  You can do that kinda cheaply.
  Like I posted earlier, I have the poultry net.  In the winter, we get a few inches on the ground, unless I clear the whole fence line, the fence will be grounded out, no sparky.  But, the wildlife around here wants no part of it.  They won't even approach it.  I've seen them go through the property and give that fence a wide berth.