How long will it be for my new dog to look after me?

hi , i brought a Doug de Bordeaux 3 days ago , he is nearly 3 years old and i was just wondering how long do you think it will be for him to understand that we am his new family and it is now us that he has to look after ?he is happy dog and seems to feel comfortable her as he sleeps well, he was under fed buy the last owner as he is only 50kilos, and the last owner had him out side , i feed him well ( i don't over feed ) play with him and have him in doors and take him for walks, i am just looking after him like the last owner should, i would like to feel that if some one came into my house un invited he would protect us, i have not had him just to guard us he is a family pet, but it would be nice to no he will look after me to