lab aggressive towards baby

Question
Hello,
My husband and I have had our 3 year old yellow lab since he was 8 weeks old. We had him fixed when he was 8 months old. He has never shown aggression towards anything and we where shocked when he started growling at our 8 month old daughter. He will growl at her when she is crawling towards him but will also growl when she squeals or makes any noise. We smack him and tell him no but this does not seem to be helping. We also have a pit bull mix we adopted from the shelter who is fantastic with our daughter and try to make a point to praise him in front of our lab. We are out of ideas not wanting to get rid of our dog but not wanting to risk harm to our daughter. Please help. Thank you!

Answer
A growl is a BITE waiting to happen.  Hitting your dog when he demonstrates this behavior is MAKING IT WORSE.  STOP IMMEDIATELY.  Praising the other dog in front of your Lab is not doing anything except, perhaps, further requiring and facilitating the Lab's response to your baby.  Your lab has NO IDEA why you are praising the other dog and, most likely, neither does the other dog.  When you praise you must know, 100%, what the dog is THINKING and what the dog immediately identifies with the praise.  You have no concept of this and you are not remotely qualified to manage this situation.  Remove BOTH these dogs from free access to your child at once.  A human infant, even a young child, is no match for an out of control dog and any dog, at any time (even the best behaved dog in the world) can suddenly react to something a child does (without any clear visible reason to you) and seriously harm, or worse, that child.  Young children, especially babies, should not be exposed at eye level (while crawling or toddling) to any dog without VERY strict supervision.  Whatever is prompting your Lab to growl (it might be rank related, it might be a fear response), you MUST separate that baby and that dog.  As you have a two dog household, you also have rank issues between the dogs and among yourselves (humans are pack members to dogs.)  My first reaction is to immediately rehome that Lab and keep it separated from your child until you do so.  Of course, this requires careful scrutiny of applicants (including HOUSE CHECK, strong (STRONG) veterinary reference and personal reference) and requires that you are honest about why you are doing so (making sure there are NO young children in the new home and none that visit.)  This will not be an easy task.  The second choice is to obtain the help of a credentialed dog behavior expert, Ph.D. or DVM (NOT a DOG TRAINER!) immediately, although even with such expert help are you willing to take a chance on your daughter's life?