6 yr old boxers aggressive biting

Question
Hello, my family got a male boxer-bulldog mix when he was about 3 months old from a shelter.  He likes to occasionally rough-house, which usually includes some play biting (he pretends to bite my hand, but his teeth never actually touch me).  If things ever get out of hand when we do this, we immediately let him know and stop it.  However, there have been several occasions where he has suddenly bitten at people aggressively.  It's usually around food, but sometimes not.  It's been toward my family members, guests, and strangers.  We now can recognize signals that he is going to do it (head low, tail between legs, jowls twitching), so we get him out of the situation in these cases.  We think he knows that when he does it it's bad, because immediately afterward (before scolding), he looks at us with that "I'm sorry" look and hides his tail between his legs.  He's already so old that we don't really know what to do to stop the problem other than take him out of the situation and put it off from happening.  However, this makes us very nervous when we have guests over or when strangers come up and ask to pet him.

Answer
Hi, and sorry for the delay in answering your question. The first thing I would suggest, is to get your dog to an obedience class. You can teach old dogs new tricks, and this very well could help your boy with is problem. Biting, at any time, should not be allowed. Do not let him even play bite, or play nip. You may want to contact your local obedience trainer, tell him your dog's problem, and see what he suggests. If you don't know of any classes, ask your vet. I wish I could give you a simple answer to make this all better, but the only real answer is to get this dog to a trainer that can help you and your dog with this problem. If you don't get a handle on this, and if your dog bites someone, you could get into a lot of trouble. In my opinion, no dog is worth someone getting hurt. I'm not suggesting that you get rid of your dog, he just needs to be taught that this behavior is not tolerated, at all. Your dog has to be taught that you are alpha, not him, and this aggression is not going to be tolerated at all. Obedience class can do wonders for dogs like this. You can make your dog sit before you feed him. If he's just walking through the house, make him sit. Don't step over him if he's sleeping on the floor and in the way. Make him move. Don't allow the play biting at all anymore. If you are out with him and he starts acting up, change directions with him, or remove him from the problem. When he acts good, praise him. You have to be consistent with your training, and keep at it. These things that I suggest are just small ways to remind him that you are boss. He really needs some professional training as well. A professional trainer can watch your dog personally, see what he's doing, and work with you. I wish you the best of luck!