Hello, the best way to avoid aerial predators is keeping the flock contained in a large covered run. As long as the run is large enough and has boredom busters to keep them entertained, they will be fine.
Welcome to BYC. We have nesting hawks and eagles here. I have large covered runs to keep them safe. My chickens don't go out of their runs unless I'm out with them. That's not to say that they are 100% safe but my presence is generally enough to scare the birds of prey away.
So sorry about your flock. Sometimes free ranging is not possible when you have lots of predators. A big sturdy covered run will keep them safe and protected, you can do supervised free ranging when you can be outside watching.