The 49ers offense has been under fire this season from all sides. The passing game, which ranks last in the NFL, has disappeared at times. The explosive, big-play attack that flourished late last year is more subdued. And fans and NFL analysts continue to ask, "What's wrong with Colin Kaepernick?"But while the offense has sputtered, the defense has remained rock solid. Former NFL head coach Herm Edwards his week even called it a Super Bowl-caliber defense.So as St. Louis quarterback Kellen Clemens prepared for the Rams' matchup against the 49ers Sunday at Candlestick Park, it was the San Francisco defense that was on his mind."Finding a weakness," Clemens told the St. Louis Post-Dispatch, when asked this week what the biggest obstacle is in facing the 49ers. "They're great up top, they've got two of the best linebackers sitting there staring you in the face and then they've got a very good secondary. Find a weakness on that defense and then please tell me about it."The 49ers rank No. 6 in total defense, No. 4 in points allowed (16.7 per game), No. 4 in pass defense and 12th in rush defense.Rams head coach Jeff Fisher said it will be a challenge for the Rams to play against the...