In addition, we had him neutered at 6 months. He had not then, and he has not since, ever challenged us, disobeyed on purpose, or even put his teeth on us. We didn't allow that when he was little, and he's never done it.
We were warned specifically about training the dog that way by the breeder. She said, "Never allow him to mouth you or your clothing or any possessions that you don't want destroyed." So, we didn't. He had constant 24/7 supervision until 5 months old, mostly because for various reasons, I was at home for those three months.
Best of luck with yours. I know we sure loved our Mastiffs.
Huh? my dog bites me all the time. If I don't like it, I bite her back!
We didn't allow teeth on us either. But, he constantly came back with his nipping on our hands. It was like a "have to," greeting behavior. We even used the hand (the whole hand) down his throat, as a negative result from nipping. It did have some good results. But, he would just let you do it and then nip the next time.