Yes, you can try hanging wind spinners or old cd's, either individually or made into mobiles. It's unnecessary to hang them everywhere, we hang a few discreetly close to areas where our birds take cover, or, we have a couple of moveable mobiles that we can move about, made of old CD's and ribbon. We feel that they do help, we've seen hawks sitting in other areas but not where the flashing spinning things are. Wild bird stores have recommended this technique to us, and it does seem to work pretty well. We also use "Bird Bombs" on occasion, they also work very well. Roosters are useful in that they are constantly on the lookout for hawks and other predators, where the hens might not be. And the roosters will warn the flock if they see or sense anything strange.Some cities are now making allowances for city residents to have a rooster under certain conditions. Guineas are good too, although I don't know if they'd be allowed in a city. Sometimes having a couple of larger birds, like geese, around, can be a deterrent . Lastly, make sure your flock has plenty of cover. You can make "hawk bunkers" out of brush and other materials, if you don't have enough in key areas.
