They quack all the time, just between themselves, or because they see something/someone. They're ducks not guard ducks.
Get a dog and a cat, and show them how to work as a team. The cat will generally see a potential intruder first because it will tend to lurk further away from the house, but when it comes running back it'll tell the dog that something is afoot. Then, dogs are gonna dog which is why we love them.
