Locking door sends out a very negative hostile message and easily leads to unwanted conflicts and misunderstanding. Old folks esp MIL are very sensitive towards ANY acts by daughter in law. Once you land yourself in such uncomfortable awkward situation, things wld only get worse if not better...I think the best way is to bring the baby To the room and lock the door. Coz given ur hubby personality, I doubt he cares as well. Though it's tiring, but at least u won't so pek chek and can also 'tune' baby back..