If they don't move, the hawks learn quickly that they're not scary. The bird scare tape has worked very well for me. I had an area the red tails were using as a bombing run. I strung scare tape across it and along the 2 shrubby areas my hens hang out around and for the last year I haven't seen...
Now if you could only get a motion-activated way to make it wave an arm or turn its head, you'd totally convince the hawk that there's a guard on duty.