Have you tried the larger Nylabone Dura Chews with bumps and ridges? Our bullie Frank has been chewing on his for a while and he is very aggressive with his chewing. There is also a dinosaur, which is good because the odd shape keeps it moving around in their mouths. We have also had luck with large deer and elk antlers which last a long time. You just need to supervise them of course because if it gets small enough to swallow they need to be thrown away. Frank will gnaw at his for hours and will just cause tiny shavings to come off. Also, we like the very tough kongs, usually in the black colors, for very strong chewers. Have you thought about keeping him busy too with something he can't chew, like a large Kong Wobbler or a Jolly Egg?