I only got Teagan at 12 weeks, so she couldn't go for walks until about 15 weeks old, and there was no way I could carry a Bullmastiff around! At 12 weeks old she was already 12kg!
I just let her meet lots of visitors to the house, and let her in the front garden to hear noises.

Hi, Millie is a sweet dog, but she was 8 months old when we got her. I don't think she had been socialised very well, the people we got her from, lived on the edge of a small village and the man said he trained Millie to come back by throwing a ball and giving it to him in the fields where he lived. But where we live is near the sea and lots of people pass by with dogs etc. Millie is so excited when she sees another dog that she doesn't see or hear anything else (including us), she loves to play. So we tend to keep her on a long lead. There are fields nearby so we take her there often. She loves people and all other dogs but we are just dubious about letting her off the lead. :smt017
Annex