Someone on the forum had chicken wire ripped off the roof of a run by a fox and either the coop pop-hole was open or it was daytime and lost all the hens.
OMG

I've got this over my run! I had 6'6" high sides to a walk in run until I had a fox attack (the devil came in over the top :evil: ) So then covered the top too. As its very large the polyprop type sheets would work out very expensive so might look at putting a second layer over it.
For mine the sides are dug 12" down into the ground & back filled with rubble then an 18" skirt around the outside. This was the best information on how to do it I could find at the time. Also if chicken wire is used it must be less than 1" holes & the thickest quality. If they can get their mouths in foxes can bite through the holes. Their teeth are like wire cutters. But the best thing is weldmesh.