Just finished building two low row covers for my winter crops. I did it as described on page 89 of Eliot Coleman's book, "Four Season Harvest". Apparently this is a French innovation - to have little loops on each hoop so you can tie a rope to hold it down, rather than burying it with dirt. This makes it easier to harvest and vent.
I used #9 wire, and bent it into a semi-circle shape a little longer than he said, actually 8' long instead of 6.5' since my beds are wider. (approx. 40 - 42" rather than 30 - 36" he calls for) I used needle-nose pliers to put a loop about 1.5' from each end, again a bit longer than he called for (1'). It needed to be longer to accomodate the cinder blocks. I pushed them about a foot into the ground on either end.
Then I laid the #30 Agribon over it. (actually this was better as a two person job, and Mr. Aubade helped a lot - both with cutting and shaping the hoops, then with laying down the fabric) I finished it by tying poly outdoor rope like a shoelace through each loop.
The first one came out too short, so I've got to staple on about 2 feet more. It had lettuce, arugula, mache and mustard greens in that bed (not pictured).
But the second try, as seen here in the pictures, seemed to work pretty well. This bed has carrots, chard and turnips in it. It didn't come out quite like I had hoped, as it seems a little wobbly - but I think it will be ok since my backyard isn't too windy. Guess we'll see how it goes. This is definitely an experiment. I just want to see how long the plants will live.