any dog that barks at the right times. a dog that barks when the kids get off the bus everyday after school and barks when the leaves blow by the window is worthless, A dog who senses hostility or nervousness is great.
WE have had a few, one a black lab the kids on the block would ride like a horse, take swimming in their pool and take all the abuse any kid could throw at it with never a growl or a show of teeth, but when something got him mad or agitated, he would pull you out of bed to make sure you knew something was up.
One night late, he pulled the covers off us and stood up and put his paws on the window sill, letting us know we had a "situation" I pulled off his collar and opened the window. he was out like a flash and had a burglar by the shin in seconds. After a brief tussel the thug managed to get in a car and was driven off. Dog walked back up to the window holding the lower leg of his pants and his left shoe, covered in blood. Cops found the burglar at the local trauma hospital with his calf muscle more or less stripped from his calf.
We have a little mutt, part jack russel and part who knows, that is the wifes indoor dog, I have a yellow lab, the lab is the muscle and the yapper is the brains. That little dog has the most uncanny nose and ears, last winter it alerted to the front yard, the only thing out there was the neighbors cat in the snow fall. Once he decides that something is not right, then the lab just walks up and pays attention. If the little one does the happy dance that someone he knows is back, then the lab will not move, the little dog barks the big one will move.
I decided sometime ago I will always have at least oone dog in the house, just need that to keep the attention level up.