I would recommend a German Shepard, they are easily trained when they are still young to not kill chickens. I trained one with my uncle a couple of years ago it took about a week. for ten minutes a couple of times a day a chicken was put in front of the pup and he was scolded whenever he tried to attack. He is now living on my uncles fruit farm (and campsite) and most of the customers love him. He is a black German Shepard though so he isn't as intimidating as a normal coloured one.
Wouldn't an all-black German Shepherd be more intimidating than one colored like Rin Tin Tin?