Bursts of agression

Question
My wife and I own a 3 year old male lab/mastiff mix. He is an angel 80% of the time. We often say he is a lap dog trapped in 120lb body. He loves to come in the morning and cuddle up in bed, or lay on the couch cuddled up next to my wife and I. He plays with other dogs well. My brother-in-law's dog kept taking away his toys this past weekend and our dog let him, never going after the other (much smaller)dog or toy. I have never seen him act agressively towards another dog. The problem is when he feels cornered he will aggessively lash out at people. He was in my car yesterday (I often take him to work with me where I play ball with him a couple of times a day, usually at least an hour). His behavior improves the more "run time" he gets, obviously. When I crawled in the car yesterday after playing with him to retrieve something, he lashed out and bit my hand pretty hard (enough to puncture the skin). When we adopted him from the pound he had a nipping problem but with a lot of home training from my wife and I he has made leaps and bounds in improvement. He would get mouthy when he wanted to play so we redirected his behavior to get a toy when he wants to play. That has worked splendidly. He was difficult to walk early on. He would jump at whoever was walking him and sometimes nip the person. But now with my wife and I he loves to go for walks and people on the street often comment about how well trained he seems. Obviously we have improved his behavior somewhat but there still is that X factor.
He bit my wife last year when he was in his kennel last year and she reached in to get something. The obvious answer is do not reach in to these spaces when he is there. The problem is: ONE we are expecting our first child in 7 months and are scared a child could end up getting bit in one of these situations. And TWO boarding him has been difficult. Twice he has been asked not to come back because he acted aggressively towards the kennel owner while there. Both admitted being shocked when he did because he is seemingly a well-behaved, sociable dog. We feel like we have failed him somehow, not providing him with adeqaute behavioral training, but can not allow this behavior with a new child in the house. We are at a loss how to work with him on these situations, especially because it does not occur all the time. We are looking for local trainers to help, but of course money is an issue. HELP! Do you any suggestions?

Answer
Dear Matt, Please read as many of my posts to others about pack leadership and aggression issues. Fear and aggression often go hand in hand. So it is imperative that you and your wife establish yourselves as the pack leaders in your home. I am glad to hear that you have made much progress with your dog, but as you know, your work is not finished. You should be looking for a canine behaviorist in your area, as not all dog trainers are educated in canine behavior. Since you know that his problems manifest themselves when he feels trapped, you have a starting point. You can set up situations in which you win and are the pack leader. You cannot be afraid or back down to him or he will win and the problem can continue or get worse. Walking him at the heel several times a day is one of the very best things you can do to exercise his mind and body. Take him for a long walk at the heel prior to your training session. This way he will have walked off some energy and should be more focused on you. You can establish pack leadership with a touch or sound, there is no reason to be heavy handed or harsh. But you must mean business and show him the you are his leader, he can trust you, and must never show aggression towards you or your family. If you have any questions about how to do the exercises to accomplish this, please seek a professional in your area. Most behaviorists are flexible with their costs and can provide you with a payment plan if you ask. Also, behavior training is not the same as dog training classes that you go to once a week for eight to ten weeks. A behaviorist will work with you, your wife and the dog to specifically address the issue at hand. I highly recommend you get someone to assist you as soon as possible. You will be pleasantly surprised at how much you can accomplish in a very short time. Please leave me some feedback and follow-up to let me know how things are going. Thank you for writing. Regards, Susan