There are some very small dork discs that can be put on the wheel and are almost invisible. I don't have them on my newer road bikes or my MTBs, but I've seriously thought about putting them back on the MTBs. A wreck on the trail can easily cause a chain to jump (and has). I've been lucky that no chains have jumped into the spokes. However, when the FSR XC was new, my son took it to the trail and came back with a smashed dork disc following a wreck. I wonder what would have happened if the dorc disc wasn't there.