Improperly attaching a fence to a tree will result in a dead tree or a broken fence. As trees grow, the fences attached to them cut into the tree. The moisture from the tree can cause the fence to rust or rot and eventually break. The fence cutting into the tree can weaken and strangle the tree. A fence should only be attached to a tree equipped with an adjustable post or beam. The fence is attached to the post or beam, which is attached to the tree with adjustable cables.
Lay a 6-inch-by-6-inch post up against the four sides of the tree so that the posts are directly across from each other and flush with the bark. Position the posts so that one of them is on the side where the fence is to be attached. None of these posts are to be set in the ground. Ask a couple of helpers to hold the posts in place while you wrap 1/2-inch cables around the top, middle and bottom of the posts to keep them from rotating or moving around the base of the tree.
Bring the ends of the top cable together so they overlap each other by 6 inches. Slide a U-bolt under the spliced cables so that the cables are cradled in the bottom of the U. Place the cable clamp over the ends of the threaded U-bolt until it is touching the cables cradled in the bottom of the U. Thread a nut onto the each end of the U-bolt with your fingers and then tighten them down with a wrench until the cables are pinched between the U-bolt and the U-bolt clamp. Repeat this process for all three cables.
Nail or screw the fencing to the 6-inch-by-6-inch post on the side of the tree where the fence will be attached. Use a hammer to pound in fencing nails and an electric screw gun to screw in screws. The fencing will only be attached to one of the posts. The other posts protect the tree from the tight cables, which could cut into the bark as the tree grows.