dog behavor

Question
my 2 yr old shepherd/ husky mix is starting to be agessive mainly toward men and some little boys, I don't know where this is coming from? we have had him since he was a puppy- very good dog, smart and easy to train, for the last 2 months starting to get in trouble more, up 2 date on all shots healthy active dog, gets lots of attention. I'm a stay at home mom with a 2yr son, we also have a 8yr old girl and 6 yr old son, plays excellent with my kids never a worry with them, last month when the problem started we had him neutered to try to remedy- relatively good results until this weekend. We went out of town for the weekend and our neighbor and her son were watching him-the dog has never been aggressive toward them before and he has known them for a year, they come over allot and very familiar with them, anyway she was getting his food and her son was standing there waiting for his mother to give him the treat to give to the dog- with no provocation the dog bite the boy hard enough to bruise him and scare the ---- out of him. The mom scolded the dog and he went to his bed in our bedroom. He has nipped before at men coming into the house, usually not friends, but workers, painters fence guys or the movers. All times this occurred un-provoked- he would go for there shoes never skin or legs- this behavior I have witnessed is the dog is not growling or barking just normal dog ( but he sneak attacks from behind very quietly just walking not to draw attention to himself) which the response we give him is yelling and he gets sent to the room.  I don't know why this behavior has started or how to fix it. He doesn't act this way toward our family, but I need to fix this to not happen to our friends or people we have invited to the house.  He's confused on when to be on the job and not on the job. Other behavior issues that accompany with this not listening the 1st time or even the 2nd. I trained him the basic commands come, sit,stay, shake, lay down, fetch, walking on the leash.  Now he's running out of the house if the door is left open, we could before leave the door open and he would stay in the door way until called same with sit and stay. He's been getting out of the back yard and running off- that never happened before. I'm at a loss, I need advice on want to do, or the dog will have to go- Please help

Answer
This is a serious problem and needs to be dealt with before someone gets hurt

I think the best way to deal with this is to call around and find a dog trainer that can come to your house,so he/she can see the problems you are having with him,and so he/she can work with you for the best way to fix this,and also to show you how to deal with this-or if you can't find one that will come to the house video tape it and show him or her

A trainer is the best way to go for a serious problem such as this,as they can see exactly what is going on,and they can show you how to best deal with it