This may depend on how tight you want it to be, and the weather in your area, mostly wind, but I just bought cheap vinyl fencing for the top of my run to keep the hawks out. My original plan was to string wire between all the posts (my run is about 30x30 square) and hope the wire would be confusing enough to discourage the hawks. I didn't work- I had a 6 week old disappear out of the run in the middle of the day. I got the fencing for like $10 per 50 foot roll (it's like 3 feet wide I believe- 2 rolls and a couple scraps of hardware cloth I had laying around covered the whole thing) at the fleet farm store. Definitely cost effective. Then I only had to lay it across the wires I already had up. I was a little worried the weight would pull the wires out, but it's been up for over a year now and survived all kinds of weather, including snow. It's attached in a few places with little pieces of wire, but not terribly securely. BUT we are almost completely sheltered from the wind in every direction, so I don't know if that would work as well in a more open place.