I put up fishing line zig-zagged over the top of my run after finding a hawk in there and it has worked wonderfully so far. Keep zig-zagging it until there are no openings big enough for the hawk to "jump" down in through. One could perch on a post or top of fence and then drip down. I also hung several CDs from trees and nailed them to the tops of my fence posts and the birds do not like them at all. Something about the glare that makes them want to avoid them. The fishing line is cheap and is not unsightly at all as you can barely even see it unless you are right up next to it. Good luck!