A local living history farm/museum has a 5' fence for their turkeys. They've taken scraps of the metal wire fencing about 16-24" wide and as long as the piece is (5'?) and bent it in half to hang over the top edge of the fence - it's balanced up there, but barely. So it hangs down each side of the top edge about a foot (here's a try at a graphic.....
X
/ l \\ bent over bit of scrap fencing
l fence
So the bent over bit hangs down each side about 12", but it's real loose and very unsteady, so any predator doesn't feel comfortable climbing over top.
Don't know if it'd help your situation (their out in a corn field, so different environment), but it's an idea.....