Aggressive Yellow Lab

Question
Tucker is a nuetered 4 year old pure bred yellow lab. He is hyper, yet playful-clumsy and tends to be rowdy. He is a house dog...spends days outside when weather is nice and is fairly well behaved. EXCEPT he is very aggressive he will attack our mini datchund, and cat-growling and snarling pinning them down, will not stop until we literally pull him off them. He does not get along with strangers, human or other dogs. Recently he went after my son-19 months old, did not bite down but pinned him to the floor and left a bruise from the impact and a scratch with teeth holes. And he went at him growling and "out of control like" until i pulled him away. He does this often. We had a black lab terrier mix that he would do this to as well. Have recently lost him 14 years old. We have to pull him off inorder to stop him from hurting someone. Nothing sparks these episodes, he just freaks out at times. I am fearful for my son and the baby on the way, along with my other animals. We have spoken to area humane societies and they refuse to take him, they suggest to euthanize him. He is a pure bred papered and all 4 years old almost 5, He has never had an episode with myself or hubby, 3 strangers have been snapped at, other animals and children.
I am at a loss and desperate, but need assurance he will not hurt my kids. I am not wanting to put him down but fearful for my family and feel we have no other choice. Any suggestions?  

Answer
This is a serious problem. and I don't have the skill and experience to help with it.  I am much better at preventing such problems than fixing them.  There is too much at stake here for me to suggest things that likely wouldn't fix the problem.  Have you discussed it with your vet?  i doubt it is anything a vet can fix either.

You could try a professional dog trainer or behaviorist.  Look for one with some training.  I have no confidence in the ones with 20 years of experience on their own.  

You could talk to a Lab rescue. They could put him in a foster home for retraining, or perhaps help you.  You may find a rescue near you starting at
http://www.akc.org/breeds/rescue.cfm