When I start seeing a hawk hanging around I take them on supervised walks around the yard or if I can't then I keep them in their covered run till the hawk moves on. I've been told by several people that having a black chicken or two in the flock is a deterrent because hawks don't like crows so they avoid black birds but I can't say if that's true or not. They also make avian netting you can put up over an area but those don't always hold up well if there's a lot of leaves weighing them down in fall or freezing rain in winter. I don't really know of any way to scare them away that wouldn't also scare your chickens.