Merry preseason, everyone. It’s been a long offseason, but football is finally gearing up again and to celebrate I’m rolling out a new series on TSR entitled “2010 NFL Question Marks,” where I discuss one or two of the biggest concerns that teams have heading into the new season. Granted, some teams have more issues than others, but I’ll primarily be focusing on the biggest problem areas. Today I’ll be discussing the huge issues the Lions still have in their secondary.

A year ago, it was easy to spot the Lions’ biggest weakness, as their offensive line was an absolute mess. But after a productive 2009 campaign and a couple of offseason additions, Detroit’s O-line is no longer an issue.

Now the concern shifts to a secondary that received an offseason makeover, but remains the Lions’ biggest question mark after a dismal performance in 2009.

Last year, Detroit finished dead last in passing yards allowed, yielding 265.6 yards per game. The poor play of the defensive backfield contributed to the defensive unit giving up 30.9 points per content and over 6,000 total yards.

To address the issue, the Lions traded for former second round pick Chris Houston, whom Atlanta had given up on after signing big-money free agent Dunta Robinson. Houston has an impressive skill set and enough talent to make him a No. 1 corner, but he has yet to put it all together for an entire season.

The biggest issue with the former Arkansas product is that he always seems to put himself in position to make the play, but rarely does. He has great speed and is a physical corner, but he’s at his worst when the ball is in the air. He fell out of favor last season in Atlanta because he had major trouble locating the ball when it was in the air and making a play on it. In fact, 66% of the passes thrown his way were completed, which is a staggering number to say the least. That said, if he ever lives up to his potential he’s going to be a solid player.

The Lions also brought back Dre’ Bly, who spent two years in Denver and one in San Francisco after Detroit dealt him in 2007. At 33, he’s no longer a Pro Bowler but he’s certainly serviceable in limited time. The fact that the Lions aren’t counting on him to be a starter is a plus.

The starting corner opposite Houston will be Jonathan Wade, whom the Rams let walk despite him being a low-cost option as a restricted free agent. The fact that a bad Rams team didn’t want him is troubling considering he’s going to be a starter in Detroit.

Compounding the concerns about Houston and Wade is strong safety C.C. Brown, who comes over from New York after one brutal year with the Giants. Over the years, Brown has earned the name “Can’t Cover,” so even though he’ll be playing alongside rising star Louis Delmas, the Lions are still in a heap of trouble.

One would think that Detroit’s pass defense couldn’t get worse than it was last year, especially after making so many additions this offseason. But it appears as though the Lions have only added quantity to their defensive backfield – not quality.