Use chicken wire only if you want to keep your chickens in one place so the predators can get them all more easily. Seriously. They ought to call it "chicken death wire."
If you don't want to use welded wire/hardware cloth on the bottom of your tractor (interferes with scratching), you could fashion an apron attached with hinges to the perimeter. You couldn't stake it down permanently, but you could weigh it down with rocks or blocks on the ends each time you move the tractor. I have something like this on my tractors, not so much for predator protection (since our suburban yard is fenced and I only use the tractors in the daytime), but to prevent our very small bantam chicks from slipping out from under the edge someplace where our lawn isn't quite level.