Some folks try to clip the coil spring on both sides. It seems to work.
Chains can be used, too (get plastic covered ones and you won't hear the clanking).
I'm a big fan of limit straps, though. You want to get the quad wrap ones, because I've seen the double wrapped ones fail before. Mine are only double wrapped, but I plan to upgrade to quad wrapped when/if they fail. They come in a variety of lengths, so once you get the mounts set up, you can measure for how long they need to be. They typically stretch an inch or two.
http://www.polyperformance.com/shop/Limit-Straps-p-1-c-747.html
Here is how mine are set up. It's basically some nuts welded to a plate that's welded to the uniframe up top, and a little tab at the axle. They were originally setup to limit travel to just before the spring is at full droop, but because mine stretched an inch or two, the coil spring unseats itself a little bit, but it doesn't fall out. There are multiple mounting points on the top brackets so I can adjust them if I want.
