Not just defense that the Texans need to look at. Here's an interesting discussion regarding special teams: http://forums.somethingawful.com/showthread.php?threadid=3368051 tl:dr version: Jacoby Jones and Steve Slaton are both horrible return men.
Reminds me of the Buccaneers during the never returned a kick off for a TD era. Oh, same special teams coach for a lot of those years... What a coincidence(and yes I realize the Texans have returned one with Marciano on the staff). 90% of the Kick returns had zero shot.
