Originally Posted by raingirl
I've been just leaving the dremel out in plain view, touching his nails with it, leaving it on near him, holding it and touching his nails when it's off, everything. I will do it for long or short periods of time, and I use lots of praise and treats when he doesn't get all nippy. As soon as he gets nippy we put it and the treats away.
Part of your problem might be that you're putting it away as soon as he says enough (by nipping).
Its going to take a long time for him to get used to it, especially if his previous home hurt him somehow (and by the sound of it they did on more than one occasion). A trainer once told me that dogs really only remember what they've done in the last 10 seconds so you might want to keep doing what you're doing, but instead of putting it away when he nips, train him not to nip and treat when he 'left it alone' or 'layed still' or what ever you want your command to be.