Can Atlanta fix its defense?

Osi Umenyiora had 1.5 sacks on Sunday against the Miami Dolphins. Evan Habeeb/USA TODAY Sports

In my preseason predictions, I had the New Orleans Saints winning the NFC South and the Atlanta Falcons missing the postseason. After watching almost every snap of Atlanta's 27-23 loss to the Miami Dolphins, I feel stronger than ever about that prediction. The biggest area that concerns me for this 1-2 Atlanta team is its defense. I have some concerns on the offensive side of the ball, but right now, the Falcons' biggest problem is that they don't have a playoff-caliber defense.

Can Atlanta fix that side of the ball?