That is an excellent question.

If done "poorly" rope tied to straight rebar will indeed come loose.

However, it isn't hard to do it well. What I've found that works really well is to hold about 2-3 feet of rope in your hand and twist a little loop right there. Put this loop over the rebar and slide it down until it is about 4-5" off the ground or lowest obstruction. Call the other end of the rope the "long" end. Then wrap the loose end of the rope over the around the rebar and over the long end once. Then wrap the loose end around the rebar again and again and again and again building tight loops downward until you've used up all but about 10" of the loose end. Make one or two slip knot at the base (pull out one of the bottom loops and pass the loose end through it, then pull it tight, repeat if you like). Finally, tie the loose end onto the long end using a bowline knot if you know it (www.animatedknots.com/bowline...dex.php) or even a square knot will work. If you are at all concerned about it unraveling, you can duct tape over the loose end (it leaves glue on the rope, but it will certainly keep it from coming loose).

This works. It works really, really well.

Naturally, if you expect force to be applied in one direction (e.g. you are securing a structure against the force of the wind) the rebar needs to be staked into the ground so that the long end of the rope is essentially perpendicular to the rebar. And, if you use 2' rebar (5/8" diameter, please) it should be pounded in so that there is about 7" sticking out. Don't tie anything in the first inch, but you can tie right down to the ground.

Remember that tie lines are a *major* break-your-neck hazard -- mark all tie lines with streamers of plastic tape or reflective mylar. Tie on two or three strips on *each* tie line, at eye level for walking and lower. It is also a good idea to pile things up under the lines, such as bikes or other gear, because that naturally discourages people from walking or riding through the lines.

If you'd like, I'd be happy to tie one up here at home and take a photo and post it to the tribe -- especially if my description isn't clear enough.