I have a 2 year old dog that is extremely aggressive. The dog is very nervous of everything and everyone. What can I do different?

I have a 5 acre farm and I wanted to adopt a dog to patrol it and keep the deer off. A good friend of mine who runs K-9 in central NJ let me know that he had a dog who was from Germany that belonged to a woman who paid $4000 for the dog, and when it was 2 years old it mauled her husband. When we went to pick the dog up we met the lady at a rest area. My friend said a neutral site would be best. He was muzzled and extremely aggressive. After 3 days of talking and walking the dog he seemed nervous but less hostile so I took the muzzle off. He walked well and did not want to bite, but when I try to get his leash off, he shows his teeth. Every morning when I get to the shop the dog is very aggressive, then I talk him down and he mellows. He seems very nervous of everything and everyone and the person who holds the leash is the only one that can pet him. It?s been 3 weeks and I had a friend of mine hold the leash yesterday and I went to pet him and he almost ripped my arm off. He shows signs of being spooked often - ears back, slouched and tail between legs, and sometimes rolling his teeth when you approach him. Then if you bend down to his level and call him, he will come after awhile with his head down. The local health dept. where the man was mauled keeps calling me and saying that they want the dog put to sleep before someone else gets hurt. He is a beautiful animal and I would hate to see him put down. I have used the electric collar and that stops him from attacking but also makes him spooked.



Thanks,
Lorenzo