This dog had bitten five people. Same MO, every time - threaten them and then rush forward to bite when their back was turned. My answer was simple - pair clicker with treats, first. Then pair "NO" with a bonk. In this case, the 'bonker' was a loose piece of terry cloth - you can see it in the video. Then negative reinforcement in the form of putting him on a leash and pulling him toward me in stages -something I learned in shelters, decades ago. Then - off leash and go back to clicks and treats. I say it's a 30 minute fix because in that time I brought him to a point where he didn't have to be handled in any special fashion.