[picappgallerysingle id="3975975"]I know that's a bold statement coming from a team that finished 9-7 and didn't make playoffs. Still, my advice to all Steelers opponents this season: Don't sleep on the Steelers defense.And I say that not just because Troy is healthy, but also because Aaron Smith is back and healthy after missing 11 games last year after he hurt his shoulder.  Smith is key to the defensive line as John Harris pointed out in this article in the Pittsburgh Tribune-Review.As Harris notes, the line has some depth with Nick Eason and Ziggy ready to play, which essentially means those fourth quarter burn outs will not be part of this upcoming season.  That crazy, smothering defense wins games-and I think we'll see a much better showing for the 2010 season.   The wildcard, literally, is how well the secondary improves over last year.  The Steelers hung onto Ryan Clark, brought back Bryant McFadden who will challenge Will Gay for his old starting role and Ike Taylor will likely hold his opposite starting spot.  The bottom line is that starters are healthy again and through the draft and FAs, the Steelers were able to build a little depth to the defense.That said, I think it's a tough battle for the Steelers to win the AFC North - they will have to play hard the entire season with both Cincy and the Ravens to battle for playoff spots.