Being very powerfully built, Bullmastiffs make for intimidating guard dogs. But they are, in fact, sweet natured, calm and affectionate.  Nevertheless it’s still necessary to have a strong lead and perhaps consider using a harness rather than collar. Prone to bloating, it’s helpful to feed them 2-3 smaller meals each day rather than one big one. Using a smaller food bowl can help with portion size and ensures they don’t overeat. Celebrity owner: Christina Aguilera.