We have shiny silver metal disks around our coop and run and they seemed to work for a while. When the girls are out on a "field trip" is when we've had a Buff killed, but not taken. Just ordered a bunch of mirrors to glue to fishing line and hang in the surrounding trees. https://www.amazon.com/dp/B01G7R51NU/?tag=backy-20
I realize this thread is over 10 years old but some things never change. I don't free range anymore but the birds do have very large pens. I put heavy duty netting over my pens because of hawks and owls. I put it up about 10 years ago and it's still good.