I agree with the others that stainless steel is the way to go. I've snared numerous animals and had a bunch get away, but none ever escaped my stainless rigs. I prefer hard wire vice woven, cable-type wire; woven might be tougher, but it takes up too much room. I recommend carrying pre-cut pieces as it's almost impossible to cut or break in a field environment; I carry pieces from 18-24 inches. As for a snare not being attended, my most successful set up to date was on a small island in the Pacific (I won't name the island in case the statute of limitations hasn't expired), where I set up a twitch-up snare with a string attached to the toggle. I activated the snare by pulling on the string from about 25 yards away in a concealed position. Long story short: I caught 9 mongooses for my team in about 2 hours, using a piece of hot dog from an MRE for bait. Like everything else in the world, they tasted like chicken. I've also had luck with small to medium game in numerous other places around the world using this technique. I've snared a few animals in unattended snares, but they were generally simple snares placed at dens or trails. My best experience with unattended snares has been with the squirrel pole. There is a reason these things are illegal just about everywhere... they work TOO good. For some reason squirrels see these things as a new toy or "Squirrel Disneyland". If they were legal, squirrels would be extinct. In a survival situation paying a squirrel killing fine is a small price to pay!
George