Some good advice already here, and remember that you have to figure out what works for YOUR dog and YOURSELF - part of the magic of having a dog I guess (or kids). Our first pup, when in puberty could bite hard, too. We found that sound or verbal commands did not work (for dog and ourselves). We took to body language, standing firm (Yang in Chinese terms, putting some energy pressure, but not too much), silently, turned towards the dog, and turning with her movements, so she knew we were actively involved in the scene. As soon as she got it and stopped, we would go soft (Yin) again and turn away to take away the pressure. It took patience and practice, but we learned a lot about how these non-verbal interactions work and what makes our miss Lela tick. We still prefer - whenever possible - body language over verbal commands.