I think just be sure you fencing has adequate support. Use lumber, not T Posts, and attach it well. There is no reason there should be any sagging with adequate support. I used 4 X 4s, sunk about 2 feet deep and spaced about 8 ft apart. I used 2" X 4" utility fencing all around, with hardware cloth on bottom and as an apron. I was a healthy sized investment, but I am way past worrying about anything 'falling apart'.
The idea that any fencing to keep in over 10 birds will definitely sag is absurd. It's not the size of the run, it's the quality of the build and how much you are willing to invest in it. My run is appx 16' X 20'. Probably cost me about $500 (More than building my coop even) but it's a one time investment and was well worth it. It could have been done more cheaply if I had the ability to get stuff off craigslist and were willing to wait until things became available there. Instead I bought everything new. Since then, I've seen lots of things on CL I could have used if I had the ability to pick them up.