To realize how important the final roster decisions in his secondary will be, all Dom Capers has to do is think back to the final game of each of his first two seasons as Green Bay’s defensive coordinator.

In the 2009 NFC Wild Card playoff at Arizona, the Packers never adequately compensated for the injury to cornerback Al Harris and got torched by quarterback Kurt Warner to the tune of five touchdown passes.

Then, last season, in Super Bowl XLV, the depth was strong enough to withstand in-game injuries to corners Charles Woodson and Sam Shields, and the Packers beat the Steelers to win it all.

“You can never have enough of those guys,” Capers said, referring to defensive backs, particularly cover corners. “You always have to be conscious you can get short there in a hurry.”

Which brings us to Thursday’s preseason finale, which is the final step in the evaluation process to determine the depth in the secondary for 2011.

In Capers’ two seasons running the defense, the Packers have kept either nine or 10 defensive backs on the final roster. The top three at each position are set – corners Tramon Williams, Woodson and Shields, and safeties Nick Collins, Morgan Burnett and Charlie Peprah.

After that, there are plenty of options.

Sixth-year veteran and special-teams regular Jarrett Bush, who came up big in the Super Bowl with an interception, could be the key player in the mix. He can play both corner and safety, and his versatility could lead to any number of scenarios.

If Bush is the fourth corner expected to play a fair amount in the dime package, that could leave a fourth safety spot to be decided amongst Brandon Underwood, Anthony Levine, M.D. Jennings and Anthony Bratton.

Levine appeared early on in camp to be making a run at the fourth safety spot, but a concussion has limited him to just one preseason game. The versatility of Underwood, a converted cornerback, could work to his advantage. Jennings had an interception in the preseason opener in Cleveland. Capers called the fourth safety spot “up for grabs.”

Then again, if the coaches are comfortable with Bush as the fourth safety, an extra player from the young crop of corners could stick. Davon House, Josh Gordy, Pat Lee and Brandian Ross are all in the mix for roster spots, but there’s no telling how many are available.

House, a rookie fourth-round pick, didn’t make his preseason debut until last week due to a hamstring injury, and he appeared to be just getting back to full speed this week. “What we’ve seen of him, we think he has potential, but we need to see a lot more of him,” Capers said.

Amongst the others, Gordy had a pick and a sack in Cleveland, Lee was the other effective Super Bowl sub when the defense desperately needed one, and Ross had a pick-six on “Family Night” and an interception in the end zone to prevent an Arizona touchdown in the second preseason game.

Of course, all these defensive backs have had their rough moments, as well, which is why Thursday night is so important for them. It’s their last chance to state their case.

The same can be said for the other position groups on defense. The defensive line, inside linebackers and outside linebackers were all hit with injuries at different times a year ago, forcing Capers to dig into his depth as well as rebuild some positions with street free agents.

“It’s not if, it’s going to be when,” Capers said regarding the need for capable reserves all across his depth chart. “We’ve got some younger guys who are potentially ascending guys. The challenge to us is how soon do we have to use them, and how prepared are they and how ready are they for the bright lights once they’re thrown into the fray?

“It’ll be just a matter of time before some of those guys will have to be playing for us.”

Especially, perhaps, in the secondary.

“Our game’s become more of a matchup game,” Capers said. “If you can’t match up on a team’s third and fourth wide receiver, you’re probably going to have a long day.”