He jumps 8' WITHOUT TOUCHING THE FENCE????? Man, you ought to put him in Grand Prix Jumpers!
There is always the danger of him chewing off the harness. Have you ever tried Bitter Apple with him? If it works like it's supposed to with him (I hear it tastes AWFUL), you could put it on the harness so he wouldn't be as inclined to chew it.
How large is the yard? Is there any way to fence off part just for him that he can't get as good a running start to go over the fence? Have you tried tilting the top part inward? It might help if it isn't straight up, but slanting inward so he has to clear width as well as height. I would definately have him neutered, though, it would slow him down for a few days anyway -- he'd be too sore to jump just after the surgery.
You don't mention if he's a totally outdoor dog -- is he? You might even have to consider using a tie-out that won't reach the fence (so he won't hang himself) made of airline cable which should be difficult to chew through. Let us know how it goes.
Just had another thought, if you try the charge to the fence, you might try taking him on his lead up to the fence and encourage him to touch it. If he does, he'll get a surprise and it might slow him down some. You'll have to do it several different places, or he'll just avoid the spots you touched. You also might consider one of the electronic containment systems put just inside his take-off range and train him to respect that. Beyond that, I'll have to cogitate on this more. Good luck.

[This message has been edited by ktreva52 (edited November 26, 2000).]