These trees were a nightmare. First off, they're on a steep bank. There's a doghouse in close proximity to the lower branches of one tree. On the other end, is the fence. It's taken quite a bit of trial and error to get it to where the cats (Pete, Pete and Pete) don't get up the trees anymore.
First, the lower branches had to be removed. Then the barrier was put up. Initially, on all trees, there was a fencing skirt, that had a six inch lip that hung down. Benny was the first to breech the barrier on a continuing basis. After hours of watching him, I'd see where he was making his way up and that part of the barrier would be reinforced. In the following images, you can see the basic barrier and then, the reinforced area. Actually, Brian added additional fencing so it would be very difficult for a cat to jump from the doghouse over to the tree. Pete was able to jump from the bank over the barrier (I told you he was Olympic rated). Adding fencing to the top of two of the trees on the high bank side did the trick.
On the tree closest to the fence, Brian ended up fencing off the area from the fence and the tree. This stopped any jumping up onto the fence or onto the tree. It ain't purty, but it works. The wire was reinforced with wood along the edges. Oh, and be sure to keep the fencing free from needles, as it starts to look like something solid to an adventurous cat. Something we need to do. And soon.