Agressive behavior

Question
I have a 2 year old Chocolate Lab, he is a very sweet dog who loves to fetch and have fun but here lately he is becoming more aggressive towards people that he knows and has saw before.  He bit a man who comes on a regular basis to shoe our horses, when the man opened the barn door he lunged at him with extreme force and attacked him.  Is this normal for Labrador retrievers?  Is he just protecting?  He has never acted this way before.  He also bit a man who came to exterminate the house after following him all over the yard and letting the man play with him, the man knocked on the door after he was finished and he attacked him also.
Please help me and give me some advice as what to do to prevent this and make him not so aggressive.

thank you
Amanda Browning

Answer
Sounds like he is protecing his house, Be sure to have him neutered if you havent already it would help a bit to calm the agressive tendensies. Also be sure he has an undated rabies vaccine if someone gets bitten and you do not have a rabies vaccine current if they sue they can get the athoritys to take the dog and have it killed for rabies testing. Keep him fenced or chained when these people come over to aviod these problmes or indoors or even crated.