take your hand and grab the side of his neck, dig in your thumb and fingers until he backs down. Make a sound with that gesture, like ssssttttt or anything thats suits you. Do not hurt him but make sure he feels it. If he ignores you or growls you must put him prone on the floor and do the same until he gives in....(he may scream and fight but hold down until you feel him release his breath and relax. Then you walk away, not him. Your hand is the mouth your fingers are the teeth. One or two episodes like this and you just need to make the sound.
Funny thing: I know people who think of training children the same way. While I am not expert on training dogs (but I do feel "successful" with regard to raising children), I have had the privilege of owning a couple in my life and found that the same five (5) easy steps works with them as it does with children:
1. Authority (make sure they understand from day one, who's boss - you start by lookin' 'em in the eye when you talk to them)
2. Repetition (you seriously don't expect them to get every new rule right off the bat, do you? Did you? Do you?)
3. Consistency (let your yes mean yes... and your no mean no - this time AND next time)
3. Affection (there's a saying that "even a dog knows the difference between being tripped over... and kicked)
5. Reward (hey, even a pat on the head goes a LONG way, although a treat... or a trip to the mall... goes a bit longer)
You say no, you mean no. Not, well sorta no. You say stop, you mean stop. Not, well stop please this time. You say what you mean and mean what you say. And you do and say things repeatedly and consistently. And you let them know you love them, because they certainly love you, unconditionally, dogs and children do. Okay, most of them (there are exceptions to every rule).
Eventually, though, the dog... and the child... get the point: "This is how we do it in this house and here, no means don't do it." Neither (dogs or children) are stupid, unless, of course, they are allowed to be stupid (by not being taught not to be), or are taught to be stupid (by our example or examples we allow them to emulate). And if you allow it or teach it, you probably deserve it.
You don't need to physically grab a dog anymore than you need to physically grab a child... UNLESS... they are in some kind of immediate danger OR you have taught them bad behavior and/or allowed bad behavior to go on to the point where your words and rules mean nothing.
I have a little dog (Louis - I mentioned him before) who listens to me, for the most part. He's still quite young (4.5 months) so he doesn't always obey immediately, but he knows exactly where I'm coming from once I use a certain "tone." My husband (a darling of a cream puff - the sweetest man in the world!), on the other hand, let's him get away with stuff: partly because he's a sweet guy and doesn't like to show aggression, and partly because he doesn't really want to bother with the training part, which I totally understand is his perogative.
So, what'm I 'gonna'do? Same as I did with the children: mine always obeyed ME.
Peace!
SA, on her own and advocating for the peaceful treatment... and training... of animals.