I'm not sure how well the disco ball idea would work. Like I mentioned above, I tried CD's (lots of them) and they had no effect. Aluminum foil in a beer bottle doesn't seem to work either. Fake snakes and owls seem to be a waste of time. I'd consider getting the appropriate "Depredation Permit" but that doesn't do any good if they aren't in range.
BTW, I looked up the laws that Brian Rinaldi posted. Those statutes are for Texas. I also looked up the laws in my own state (Arkansas), and it looks like one has to get a federal Depredation Permit to deal with hawks. Information on how to do that is contained in the thread that Phoenixsw posted above. Doable, but I was hoping for an easier and more local government solution. The whole works seems like more trouble than it's worth. I guess totally birdnet-covered runs are the only surefire option.