Positive Reinforcement is very important.

Positive reinforcement is also very important! Because the Bullmastiff is a people pleaser, he will repeat actions you enjoy. By screaming and shouting at him, he experiences that you are excited and will do it again. By ignoring the wrong doings and praising the actions you like, he will do more and more of the right things. For example as a puppy you need to take him out every ½ hour to 1 hour. He will soon learn what it is all about. If he has an accident in the house, clean it up as quickly as possible with out him seeing you doing it. But a while later you should take him out again. I have trained my dogs like that and within a short while they knew what it was all about and never had an accident in the house.