Well, I've owned 3 bullmastiffs over the past nearly 20 years, and I've learned, as many will agree, that you can't get rough or lose your temper with them. Training starts the first day you get home, and I like the "nothing in life is free" method, which means you basically own everything in the house, all the toys, all the food the doorways, the stairs, etc. They need to sit or do something before you feed them, give them a treat, give them a toy, let them out or in the door, etc.
These are very stubborn, independent thinking dogs who were developed to make decisions for themselves, and that is exactly what they do. Depending on the dog, they are not particularly eager to please, but they enjoy doing what you want, to a point, lol.
Rather than "dog proof" your house, let them have an opportunity to fail in front of you, so you can correct the behavior. We could leave food on the coffee table with us out of the room and our dogs would not take it, simply because people food belongs to US and they wouldn't dare. It takes time, and the dog will go through a teenage phase that will drive you nuts, but patience and consistency are important. Obedience classes are great. Socialize socialize socialize, oh, and socialize. This dog will be large and powerful and you don't want it to be nervous or fearful in new situations. Take him everywhere you can. We like the classes that train for Canine Good Citizen, because it exposes the dog to many situations and helps the dog achieve a bombproof nature.
We have kind of a strict attitude when it comes to training (dogs are not allowed to beg or look us in the eye when we're eating, for instance) because when we got our first one we had a 3 year old and we were petrified he'd knock her down, step on her, bite her, etc. so we stuck to a program and it paid off. We then had twins later on and we've continued this method for all the dogs we've ever had, so our dogs never took food from kids or bowled them over in play.
I think you'll find that you've got a wonderful companion on your hands, and don't be surprised when you want another one! We never want to be without one.
Thanks in advance Oh and Ruger has been great so far. 
