With the way society is turning out these days, people have a tendency to get dogs for protection. They should still take responsibility for the training and well-being of their dogs.
Of course, years ago, I used crayons to print up a "Beware of Attack Cat" sign. She was an indoor-outdoor cat at the time. And quite fierce about protecting "her" property. There was one door-to-door salesman who quickly changed his mind about my front door ... only because the cat jumped on the railing around the steps, sat down, then started growling at the poor man. He backed away and left.
Thankfully, she was as patient as she was ornery.