As a kid I once flew a kite with almost 1,500 feet of kite string. A quarter mile or so. It sagged quite a lot but we estimated it was about 350-400ft up or so in a field. Then a crop duster showed up.
I put the string between my legs while a fiend held the spool and ran as fast as I could to bring down the kite.
We were also about 1 mile past the end of a air force runway.