I haven't noticed the Mastiff having too much of a problem with wanderlust. We had a fenced in yard so I'm not 100% about that, but I took him off leash all of the time, and he never made a break for it. My St. Bernard is the same way. Could be due to the breed, could be the training, although I think I might lean more towards the breed because our Shiba Inu will bolt at the first chance she gets!