Peter was our next problem kitten. He could climb anything. He never seemed to be interested in leaving the yard, but did want to catch one of the rats that lives in the trees. It wasn't uncommon to find him fifty feet up in one of the pine trees. Needless to say, it was a very unsettling time for me. Every time we thought we'd blocked access, he was back up. Knock on wood, he hasn't been in a tree in months.
This tree had a special problem for a barrier. Notice the doghouse to the right of it. It was pretty easy for a cat, like Pete, who is an Olympic caliber high jumper, to get over the barrier we had originally put up. After some thought, Brian came up with another barrier.
He used the same garden fencing as on the rest of the barriers. To strengthen the sides, so that it couldn't be bent down to allow a cat access, he put a piece of wood, cut to the size of each side, through the openings. He also held it up with string from a weed eater.