I wouldn't mind at all having more (or other...or better) defensive stats to attibute to DST. I agree that 3-and-out is a reasonable measure. However, any stat you're going to use has to be readily available. If 3-and-out numbers are kept, I haven't seen them. What about a sliding point scale for first downs allowed? Maybe max points for 10 or less and no points (or negative) for 25+. Certainly there are still mitigating factors, but I think it would be a reasonable indicator of an effective defense.