I just had to share this picture because it is so funny. If these are your dogs, I am not sure that The Great Wall of China is going to do a whole lot of good.
I am focusing my suggestion on the situation where the dog can jump up, grab the top of the fence, and wiggle themselves over. In this case, your fence is almost high enough to act as a proper deterrent, but it is giving Wolfie that one "paw hold" he needs to get to the other side. Here is my idea:
What you want to do is to remove Wolfie's ability to grasp the top of your fence. What he has already shown is that he has the ability to jump high enough to get to the top of the fence. What you have to do is to take away his ability to successfully hold on to the top of the fence. Let's make it slippery!
- Take 2 x 4 lumber and cut them into 6 inch lengths.
- Drill 1 1/4 inch holes in them in the direct middle.
- Attach the poles so that they overhang into the yard and the holes are just on the yard side of the fence. I would attach them about every 3 feet.
- Take 1 inch PVC pipe and string that through the holes. You will need to attach the pieces of pipe with PVC glue and the appropriate F/F fittings.