Once, ar her former home, she was expecting someone but had to run out for a brief errand. The person let himself into the house and her Mastiff, Hopi, and Rotweiller, Tai, ran to the door. They confronted the 'intruder' and through barks, growls, and menacing looks, cornered him against the wall. Attempts, no matter how subtle, to move towards the door and leave were met with rapid teamwork. Hopi's eyes were so good that once at my house she set to barking. I had to look hard but I figure it was about 600 feet away, a fellow was walking on his roof. Sadly both dogs have since died.