Hi, To my opinion and speaking for dogs like CO, FILA, BOERBOEL, PRESSA (the real ones at least and not the “shows” mongrels) this reaction should be consider VERY POSITIVE. A well-bred DDB (speaking working wise of course and not for shows and this is the only way to breed well such dogs to my opinion) should not be consider far from the aforementioned breeds. People should understand and educate about guard dogs breeds before they get one and SHOULD NEVER own one if they consider only for a pet. They can choose from another breed. They have no right to contribute to destroy one, especially if they start to breed guard dogs for pets! A guard dog though can be trained or socialized in order to accept family friends tends and SHOULD display tolerance by any cost, ONLY to family members. The guard dog does not understand the term "brother in law" this is meaningful for us humans. In his eyes is a familiar to the family person which been "forced" to accept him. This does not entitles (and as a matter of fact you should not allow in first place) your brother in law to HUMILIATE the guard dog in such “brutal” way. Do not get me wrong try to see it through your guard dog's eyes. If your guard dog allow him to treat it this way what is the next step? To just barking in case that lets say (hypothetically of course) attacks your wife and his sister? This is not what a guard dog does and I hope you did not get such a dog for this purpose because it’s all wrong. This is what labrador does and there huge major distance in the between, a distance that someone should be aware for before choosing a dog. The decent guard dog OWES TO ITSELF, TO THE BREED AND TO THE ANCESTORS OF THE BREED, both dogs and humans that they are “responsible” for the creation of the breed, TO KEEP AN EYE on any visitor no matter brother, sister, relative or well known friend. OR IT IS A MEDIOCRE GUARD!!!!!!!!!!!!!!!!!! IT JUST UNACCEPTABLE WHAT YOUR WIFE DID and all the way around it is an honour for the breed what your guard dog did, some people they spend lots of money to teach their guard dogs to degrade themselves as a lower member in hierarchy within ONLY AND STRICTLY speaking for the family and to express great dominance and aversion against anybody else. Should be consider a disaster for a guard dog to evaluate itself as lower than anybody else but its family and your brother in law BY A GREAT JUDGEMENT out of your dog he is placed exactly there where should be. Of course it is whole family’s responsibility to educate about guard dogs reactions and not to put in danger any innocent person. This is just my opinion and of course I do not claim to be right necessarily, every one has its own perspective after all. This is mine. Regards