The bullmastiff is one of the most reliable and loyal guard dog breeds in the world. It was bred specifically for the purpose of guarding, a job that it does very well. They already have an innate sense of their territory as well as who does and does not belong in it. Their instinct will instruct them to ward off intruders although they will readily accept strangers into friends if they see that their masters and family do the same.

The ideal owner for bullmastiff breeds are those that can command respect and are capable of training the dog enough to do so. The dog is territorial and possessive by nature, but in the household he must know that he comes second after his family. Bullmastiffs should belong to owners who also possess personalities strong enough to command the dog and are consistent as well, otherwise this could pose a problem.