I think it is a multitude of things that keep coyotes away from my livestock and crops. I use:
Solar powered nite eyes, was skeptical at first but worked great
Sprinkler(motion activated), works very well as it is loud and disconcerting. A bit pricey though
Secure coop/pen, self explanatory
Dog: I have a dog that marks his territory around the garden, orchard, etc., things have been much easier since adding him into the equation
Fencing, using electric is always ideal, but for some people it is not an option, dogs and kids usually learn to stay away fast
Paintball guns/BB guns: work amazingly well after a shot or two at keeping predators at bay
Also, male urine around the yard helps, coyotes smell the testosterone in the urine
Strobe lights, flashy and sometimes unsettling to other animals.
Please do not resort to poison. I understand as a last resort if an animal has attacked or shown interest in humans, but it is very risky. Too many animals: dogs, cats, even young kids, will/can get to the poison and may eat it. Plus, there is no guarantee a coyote will actually eat it. IMO shooting is the most humane way if you have come to the conclusion that removing the predator will help your flock or at least relieve the pressure. I won't voice my opinion on "getting revenge," I don't want a debate. Anyway I hope for the best for you and your flock. Good luck!