To Lab or not to Lab - that's the question

Wow am I in a tight spot. My son is about to turn 18 years old and he tells me the only thing he really wants for his birthday is a yellow lab. Here's the thing, I already have one dog and he's about 3 1/2 years old. I have a relatively small yard. I know my dog , Bear, would probably actually love to have a brother but my husband absolutely hates the idea. What's a mom to do ?!