Ditto on the rebar: our local rental company uses them exclusively in setting up their very large canopies/tents. Their rebar-stakes have a washer slipped over the top end, then slid down about 2" from the top, and spot-welded in place at an angle to keep the tent rope from sliding up and off. A couple of half-hitches or bights around simple rebar would retain as well, but make it harder to take up slack.