I've got a big old Chinese Tallow tree in my run. We enclosed the run in chicken wire (hardware cloth on the bottom 3 feet) and just wrapped the wire around the tree. It's been 5 years now and we've had to re-wrap a couple of times because the squirrels make a hole, but nothing bigger has gotten in. At night, they're locked up in the coop, so any coons or possums can't get in there.