Rod Marinelli has his work cut out

IRVING -- Rod Marinelli is one of the NFL's most respected defensive coordinators.

He's considered an excellent teacher and motivator. Cowboys owner Jerry Jones and coach Jason Garrett also must believe he's a miracle worker.

They've given Marinelli precious little to work with as he prepares the Dallas Cowboys' defense to handle the San Francisco 49ers' rugged offensive unit.

The unit's only No. 1 draft picks are Rolando McClain, who's retired twice in the past year, and Morris Claiborne, the epitome of a bust during his first two seasons.

Henry Melton is the only projected defensive starter who's ever been to a Pro Bowl (2012), and he missed the last 13 games of the 2013 campaign after tearing his ACL. A groin injury slowed him during training camp, and he missed the entire preseason.

And Melton is supposed to be the unit's star, because he plays the most important position: the 3-technique. Melton plays on the outside shoulder of the guard, where he's supposed to use his quickness to disrupt running plays and collapse the pocket when he rushes the passer.

Melton did that before the knee injury. And he did it when surrounded by a group of talented players in Chicago. We haven't yet seen him do it while wearing a blue star on the side of his helmet.

The rest of the defense is composed primarily of journeymen -- dudes trying to resurrect their careers and fringe NFL prospects.

Talk to enough folks at Valley Ranch and they'll tell you they believe Marinelli's scheme will give each player an opportunity to succeed.

That didn't always happen last season. The decision by then-defensive coordinator Monte Kiffin to leave Brandon Carr man-to-man against Calvin Johnson much of the game against the Detroit Lions is all the evidence you need of that. (Johnson finished that game with 14 catches for 329 yards and a touchdown, and Carr was never, ever the same.)

Marinelli's scheme is simple on purpose, so players can play instinctively while also limiting their mental mistakes. Garrett will tell you this group of players will play with relentless effort every snap, and there's so little difference between most players that there won't be a noticeable drop-off when players rotate into the game.

And if things go right, help will arrive soon:

Anthony Spencer, who missed all but one game last year, is expected back on the field in about three weeks as he continues to rehabilitate from microfracture knee surgery.

DeMarcus Lawrence, a second-round pick, will return from injured reserve in about six weeks.

• Defensive lineman Terrell McClain, who missed all preseason with a high ankle sprain, could return in a couple of weeks.

• And cornerback Orlando Scandrick will be back from his violation of the NFL drug policy after four games.

The Cowboys set a franchise record for yards allowed (6,645) last season. The franchise record for points allowed (436) set in 2010 might get broken this season.

No records of futility are safe.

Garrett was asked what is the best aspect of the Cowboys' defense.

"We have a lot of different combinations of guys who come from a lot of different places," he said. "We drafted guys, we signed guys, and we brought veteran players in.

"A lot of guys have been here from the start. Some guys have been here more recently. We just like how that group works. The guys who have been with our team understand what we're asking them to do defensively. And the more they do it, they're getting better at it.

"We like the competition. We like the number of different guys playing on the defensive line for us, the number of different linebackers. All those guys are fighting for a role, and we think that's good. And we think everybody has benefited from it."

Notice Garrett didn't mention the run defense. Or the pass rush. Or forcing turnovers.

Actually, he didn't mention any players by name.

Not one.

And that tells us all we need to know about this defense to start the season. The Cowboys can have all the try-hard guys they want, but it won't make a difference most weeks.

This game is about talent. The Cowboys simply don't have enough, not even for a miracle worker like Marinelli.