What's a good farm dog ?

I have a small farm and I'm looking for a good breed of dog to keep an eye on the property. It needs to have an attitude about his territory but is copacetic about the critters that are supposed to be there such as chickens, ducks and other penned poultry. It needs to go beserk about predators such coons or birds attempting to fish out of a small pond. I figure an attentive dog would be far cheaper than any other measure I could implement for farm security. An intimidating and attentive dog; even better.