I have a "hot" wire running off my horse corral to keep the dogs off the rodies along my fence line & garden, it's solar powered. For your purpose you might want to concider putting something on top of that wall, maybe some decorative latice or something.
I don't know if setting up a hot wire infront would keep him off, you could probably set the wire on top. My dogs do respect the wire, it's tuff when they get zapped for the first time. My wire is a pulse not a constant so unless you hold it you wont get zapped, wet noses on the other hand....
Your dog would have no problem getting over that wall.
Going to get the rock tonight after work. It just seems like the easiest solution. I'm pretty sure it's just that corner that is the problem.