Hard as it is to do, the advice I've always been given is to show no reaction when Timber bites. I really don't think he understands how damaging his bites are to me. Several have told me that the more reaction you give them, the more likely they are to repeat the behavior to get a reaction (reminiscent of small children). So, when Timber does give me a bite, I do what Luvparrots suggested. I say "no bite" to him sternly then clean up the blood trail and my sorry self without further fuss.