This is a good article that takes you through the days before and just after the birth of your baby:
http://www.familydogonline.com/Articles%20of%2 0Interest/Introducing%20a%20Dog%20to%20a%20New %20Baby.htm
The most important thing is remember your dog is getting on in years and make sure that he has a place to 'escape' to and make sure that the children around know that when he goes there that they MUST NOT disturb him in any way.
Don't forget that at 9 years old he is probably the equivalent of an 80 year old man - would you let a toddler jump all over an old man and pull his ears/hair etc?
A dog only has one way of saying he is not happy or in pain - that is with his teeth.
To be honest with the lifespan of a Rottie you will be extremely lucky if you still have him when the baby is toddling.
I would not rehome him (even if you could), it is difficult to rehome a young Rottie and you would find it impossible to find him a good home, unless you have VERY good friends or relatives that are willing to take him. If you feel you cannot cope or trust him then to be fair to him (I know this is not going to be popular), but to be honest I would have him quietly put to sleep whilst he has people around him who love him dearly, you owe him that much. To try and rehome him to strangers at this stage in his life would be very unkind.
Having said that I am sure that you will be OK if you follow the above articles advice and bear in mind the dogs age.
Good luck with your new arrival.