We tend to forget that our dogs are mirrors of our reflection and even though they are unable to rationalize they can sense the excitement in the air.
Dogs are descendent of the wolf family and genetically used to following a pack leader. So your bond and leadership position with your dog is a crucial issue. Nine months is ample time to strengthen your position with your pet. But if you are unable to get through to him with the rules and boundaries then work with a professional. The usual paw nudges and nips to get your attention should be stopped because this may harm the baby.
As you are preparing to welcome the new arrival to your home the first condition should be not allowing your dog into the nursery. Once you have the place set up, invite him in for short supervised period to sniff around. Then immediately send him out. Repeating this will give him the message that the room is not his to own and belongs to a pack leader.
Bring something that belongs to your baby home first, maybe his blanket, for your dog to get accustomed to the smell. Remember the blanket is for him to smell only and not to play with, so that he gets accustomed to the new smell and recognizes the smell when the baby comes.
The day you bring home your baby, remember your dog will be very excited to see you after so long. So it’s better if someone else holds the baby while you continue with the usual greeting routine. There are chances he might bark at the baby till he relates to the scent.
The person holding the baby should be calm, thus indicating to the dog that the baby is a part of the pack leader. Maintain a respectful distance between your baby and him. You need to be very patient and calm with your dog.
He needs to get accustomed the shared attention and love. Set down some ground rules, like it’s not ok to muzzle or paw the baby. Give him treats so that he learns that the presence of the baby brings good things. If he does something inappropriate reprimand him calmly.