Wow, I've been reading through the dialogue between Sheprano and Katran, you guys got a little intense there, but I think that Sheprano (despite coming of kinda strong at first) is giving some good advice, although I will disagree on one point... I don't think obediance class will do too much for the chewing itself, as this is a very strong natural urge for a dog of that age and breed, although a trainer might help offer suggestions. For instance, we ignored our trainer's insistance that our puppy was not ready to be left alone in the kitchen uncrated, and we got our walls eaten. Then we listened

If your dog isn't one of those dogs that loves the taste of Bitter Apple, you can try spraying it on stuff you don't want the dog to chew, but the taste goes away very quickly, so it might not work. If you don't want to crate the dog, again, I'll mention the ex-pen. Works much better than baby gates, since baby gates are usually wood, which my dog eats. The other advise Sheprano gave about the toy box, and catching the dog in the act, etc. is what we've been doing with our dog, and we've definitely made progress.
A couple other points: Not a big fan of cow hooves if your dog is truely a power-chewer, we gave one to Scout for the first time last night and she put a nice, sharp, jagged crack in it so we had to take it away. Try filled Kongs, they really are indestructable (although the dog will most likely lose interest the second the filling is gone)!! What sort of bones are you giving that your dog can eat so quickly? Beef bones are stronger than ham or lamb, my dog can destroy a cell phone in 10 seconds flat, but beef bones last forever. For other chew treats, try Flossies in addition to Bully Sticks, I find that a Jumbo Phat Flossie lasts longer than a 6" bully stick, and Scout chews them more thoroughly (if I don't get the last 2" of the bully stick away from her in time she'll swallow the rest whole!). I also like a product called N-Bones (not made by Nylabone), they don't last super-long, but my dog is wild about them and the ingredients seem healthy. Oh, and a frozen carrot stick shoved in a Kong should keep the dog busy for a little while, too.
Toys: I wouldn't give up on hard toys just yet, since that's really all you can leave unsupervised with a power-chewer... soft toys become a choking hazard as soon as the dog gets the stuffing exposed. Nylabones come in lots of shapes, textures, sizes, and flavors, so maybe you haven't found the right one yet. Also, my dog is a big fan of the Greenie's Smart Chew toy, get the dark green one for agressive chewers. They are mysteriously melon flavored, which you wouldn't think dogs would be into, but Scout likes it more than her bacon flavored Nylabone, go figure! As for soft toys, I do buy them for Scout because she likes variety in what she chews and just LOVES ripping stuff apart, but don't bother with expensive toys. A $20 "indestructable" soft toy will be destroyed just as quickly as the $2 toy in the bargain bin, so go for cheap... but again, use supervision! For a compromise between hard and soft, get a couple rope toys, my dog loves to both chew on them and play tug-o-war and fetch with them. Just make sure the dog doesn't get it unravelled-- a big dog should be able to pass the little threads that come off just fine if they're swallowed, but a big clump of thread that gets swallowed would cause some problems (in this case, DON'T go for cheap, as it was the $3 rope toy that Scout got unravelled, the more expensive ones don't do this.). I also like Stacita's toy alternative suggestion... Scout's favorite toy in the world is a cardboard box! She'll spend hours ripping apart the box from a 12-pack of beer or soda, until there's nothing but cardboard confetti left
I also had a question about "muzzle harnesss"... do you mean something like a Gentle Leader or a Halti? These are NOT muzzles, and shouldn't be confused with them. I use a GL with Scout, and have had good results, but I'm annoyed that everyone thinks its a muzzle, so I'm thinking of switching to a chest harness. An actual muzzle isn't designed to stop pulling, and honestly, you shouldn't be walking your dog with anything that prevents it from opening its mouth fully, as this restricts the dog's ability to pant and could cause the dog to overheat.
Ok... that's my very long 2 cents