I live in Hawk central over here in Georgia.... the poo described near the carcass of the dead bird is a calling card often seen at Hawk kills. And hawks will return to a carcass if they think they can continue their meal.
I think you have to have a combined strategy. Not alot of mention about shrubbery as a hawk strategy. My birds free range all day and I rarely lose any (knock on wood). but I have alot of shrubbery and other yard furniture , fence lines. Fence lines with shrubbs. Shrub plantings around trees. The chickens generally seem to be aware of their escape options and will keep near the cover. They will hang out all day in the bushes some days. I can tell when hawks are around because of the behavior of the chickens. They will cross open areas at a run. No loitering. I rarely am able to spot the hawk in question, unless it is in the air.
Also I have a couple of roosters. They are very vigilant and sound an alert when a predator is sighted. The hens immediately scatter to the nearest cover. It is impressive to see.
I also have dogs.... I think my Australian Shepherd is to some degree cognizant of hawks and will keep them off. But he is getting older and would rather hang in the house.
I have never heard of a hawk attacking into shrubbery to get at birds. Maybe if desperate. I also think an older hawk will consider his chances of getting to eat his meal and not just killing it. Roosters and dogs make it less likely they can enjoy their kill. I have lost small young chickens to Coopers Hawks...Young hawks are much more careless or heedless than older hawks. I would not expect such good results from hanging up old CDs unless they were navigation obstacles like barrage balloons.