Major is telling you this dog has a problem! He needs to be retooled, I would start here, pretend you just got him...start over:
I just got a rescued dog – what do I do? | stickydogblog
And this should prove helpful:
Wheres my sanity: Sit on the Dog, aka: The long down
And this should prove helpful for awhile I'd combine it with the 'Long sit" for awhile:
A Great Small And Lightweight Nylon Mesh Muzzle
Consider it more of a training muzzle, not as secure as a basket muzzle but as long as you have eyes on the dog it works. It should be helpful in moding his behaviour. But don't short cut the other stuff! Dog can quickly learn ..he can get this muzzle off! But it's a OK muzzle on dogs that aren't wildly out of control! Sort of like... OH muzzle off?? It's go time!
I been where you are only difference is my rescue took 7 months to turn into a "tool!" Had I followed most of the links I posted, before learning all this stuff, the hard way, maybe I would not have had stitches??
More links here in post 8: And especially "Who Pets my Puppy or Dog.":
New Dog, Very Challenging
And multi dog homes:
Introducing a New Dog into a Home with other Dogs
Two or More Dogs
So safe to say...your not alone! Sit down the ground work on who is in charge is the first step! You can't correct a dog who has little or not enough reason to respect you as a leader! Well I guess you could but...not recommend!
It's going to be alot of work!
Oh yeah one more look at Rank Drive here:
(Elements of Temperament, by Joy Tiz )
Good luck and yeah welcome aboard.