Jason Marshall wrote:

You're all a bunch of smart guys, maybe you can help a poor Canadian
hay farmer find or make about 1000 cinching tie-downs similar to this:
http://www.inlandtarp.com/Super%20Cinch%20Tie-Down.htm

I have tried many methods of securing tarps but nothing has worked yet.

I have tried dozens of mechanical gadgets over the years and more than a
few elastic based systems. Nowadays I simply use a piece of rope
through or around something (gromet or tie-down loop on trailer or tree
or ...) and secured back on itself with a Midshipman's hitch or on
critical and/or very slippery ropes, two of them separated by a few
inches. (See "Ashley's Book of Knots", shown as knot number 1027, 1855
and 1993.) e-mail me (remove the obvious) if you want me to send you a
photo of it in use. A major advantage of this knot is that it can be
tied in a rope under tension without giving up any slack. I have been
using this for many uses over the last thirty or forty years and have
yet have it fail. It must be kept under tension, though.

Ted