Lab is aggressive

Question
Can you tell me why my lab is aggressive toward strangers. He was not like this till he turned 2 now he barks and will snap at any stranger that walks up to him and if he is in the trick and some one comes near the truck he acts like he wants to tear them up. He is not like this toward family members or other dogs I have grandchildren the love to lay with and on him with no problem he is very laid back at home and around his family.

Answer
Follow this plan IN ORDER: exercise, discipline, AFFECTION: (WITH NO VERBAL SOUND, PREFERABLY). Walk him twice a day, at least 30 minutes each time. If you must skip a walk, replace it with a treadmill, but don't leave your dog alone on the treadmill and leave the house, it's dangerous. I recommend the book " Cesars Way" by Cesar Millan. You can get it @ Amazon.com. This is definitely the book for you, and I recommend it to all dog owners, if you want your dog to live a healthy, happy life.

Never let him walk ahead of you. He is permitted to walk beside you or behind you, but never in front, as this is a sign of dominance. If you let your dog walk in front of you, ever, not just on walks, you're telling him he is the leader. Unless of course you give him permission. Never let him jump on you either ( Another sign of dominance). If he ever does anything you don't approve of, lay out a flat hand, curl your fingers a little bit, and bump him firmly, but not too hard. Follow it with a firm "chtttt". This is like a dog nip, which does not hurt him in anyway, but just gets his attention and startles his. It tells the dog this behavior is not allowed. Hope this helped!!!