Stand with a brightly colored broom and wave it wildly. The ones we got circling decide to leave when we do that when we got the chicks out. The crows who have their heart set on a chick dinner however don't mind this.
Best thing to do is to make them a good sized covered run
I would say it is time to build a run with a cover over it. If you know that the hawks are going to get your chickens, then you need to take a proper course of action to protect your chickens. They are virtually helpless against predators like that, so the best thing to do in your situation is to build a run that is covered and keep them locked in. I know that sounds like a boring life for you chickens, but if the run is large enough they will be just fine and much safer and happier than being eaten by hawks day in, day out.
You are also absolutely correct that it is against the law to shoot a hawk or any other bird of prey.
Hey! This is a fantastic idea too, but one that would take awhile to establish unless you can find a full grown Heeler, Pyrenees, German Shepherd, or another livestock dog that is ready to do the job!
What about firing a noise shot? I don't know anything at all about it, but I saw the noise shells at the feed store today.
How about shooting the hawks with paintballs? Or maybe getting a power sprayer and being ready to hit them with that? I encouraged the crows that come around and they hang out because I feed them bread. They keep the hawks at bay, somehow.