Great Dane Pup Protective?

Hi I have a 4 and a half month old Great Dane pup whose showing some signs of being protective of not just our house but me. If he hears a strange noise in the house he'll get up bark a lot then growl. But now its not just the house its me as well. If anyone comes up to me and hes there he'll start doing this deep throated growl and it does scare people a bit. I mean imagine when he's older that'll really scare people. And he doesn't do this with everyone, when my fiancee walks him hes all tail wags and fun when other people come say hi. But if I walk him and a stranger comes up he'll growl and kind of prowl around until I tell him to stop it, and even then sometimes he won't quit. I'm wondering if I'm doing something wrong or coddling him? I spend most of the day with him by myself could that be it? If anyone has advice let me know (Oh and he has no signs of aggression in his breeding both parents are big babies and the sweetest things)