The mastiff type pups that I have come across in the past - definitely march to a different drum to other breeds.
One thing I have found - as 'Sean', 'Bernie' and 'dhru' have found - repetition bores them to tears !
Their way of thinking is - I sat correctly, got my treat - oh OK you want me to do it again ! 3rd time - forget it ! Pfffttttt - I can do it - why do I have to keep on doing it - I know how to do that - let's move on !
So all I can suggest is to mix up what you want them to do, keep the training sessions really short and change your training area on a regular basis.
Also love the breed and all of its' varieties ! So have fun !smiley-eatdrink004.gif