This is the topper my hubby and I made for our privacy fence. I know it doesn't look like much, but it has worked wonderfully well. We have only had a couple of instances when one of the cats managed to get over it .... and it was only if a piece of furniture or something was too close to the fence!
Keep in mind also though, that our kitties are never left out for long periods of time, or when we are not home! I wouldn't probably recommend this as a permanent means for safely keeping a cat in your backyard full-time!!!