Gaiters for Trail Runners
Some folks may not know what gaiters are. Old-timers might call them "spats." Gaiters are fabric "wraps" for the end of your legs that help keep the crud out of your shoes on trail runs. Crud can cause friction. Friction causes blisters. Gaiters are not meant to keep water out of your shoes during water crossings, but they will keep the "occasional splash" out, though. (Don't jump to the conclusion that GoreTex shoes with GoreTex gaiters will keep water out during stream crossings...BECAUSE THEY WON'T).
I rarely use gaiters. I only use them for severely sandy courses like the Javelina Jundred, or mountain courses with a lot of "scree." But when I do use them, I use the lightest weight, most stretchy, and most breathable type obtainable, with the least seams to rub on your legs and ankles. That type of gaiter tends to keep your feet drier, because they trap less sweat (or wet) underneath the gaiter and in your shoes and socks.
There are more than one type of ways to attach gaiters. Most of the commercially available gaiters use under the bottom of the shoe strap type. The straps on these tend to wear out after only 20 miles or so on our local rocky trails. For strap-type gaiters, I replace the nylon cord (that comes stock with the gaiters) with stainless steel multi-filament wire and "swage" some special fittings onto the ends of the wire, attaching them to the gaiter's grommets at the same time. This is a pain in the butt, but it works.
But there are light, inexpensive and STRAP-LESS gaiters that I would rather recommend, instead:
Dirty Girl Gaiters http://dirtygirlgaiters.com/
Gaiters By JoeTrailMan http://www.joetrailman.com/
Other pertinent gaiter information:
In the Kansas City area, Garry Gribble's Running Sports is now carrying OR-brand nylon-fabric gaiters.
Here's what some other ultrarunners say about gaiters: http://www.ultrunr.com/gaiters.html