I double fenced my run with 2"x4" field fence on the outside to keep the large predators at bay, and I used 1/2" hardware wire on the inside. There is a 3.5" gap between the 2 fences (run has 4x4 and 2x4 construction). I have caught raccoons trying to get in, and even had a bobcat climbing up the outer fence looking to get in.
