Defenses are hard in general. I don't like total yards, for the same reason I don't like the NFL rankings based on that, as teams are content to let up yards if need be when ahead, just not points.
3 and outs would be cool, like .5 points for each three and out forced. Although, the other problem with that is, did you really do that well if you let two first downs, then a three and out?
The opening scene of the movie "Saving Private Ryan" is loosely based on games of dodgeball Brian Dawkins played in second grade.