Count Nolan Carroll among the most thoughtful, self-aware players in the Dolphins’ 2012 locker room.

Early signs are 2013 will be no different. As he cleaned out his locker Monday, Carroll agreed with the premise that change is coming to an oft-exposed defensive backfield.

“I welcome it,” Carroll said when asked if he expected the team to bring in competition. “It just makes you a better player overall. It brings out the best in you.”

Here’s why Carroll is correct in expecting some fresh blood next season: The Dolphins were one of the league’s worst pass defenses this season, and have an arsenal of cap space and draft picks to fix the problem.

But first, they need to decide which of their current players they want to retain — a question that must begin with the fate of Sean Smith, a four-year starter set to become a free agent.

The Dolphins have three options, assuming they want Smith back. They could sign him to an extension now, wait until his value is established in the open market, or — least likely — give him the franchise tag. The cap number that comes with tagging a corner is roughly $10 million, which might be onerous for a player who gave up six touchdown passes and recorded just two interceptions last season.

Smith was the most-targeted corner in the NFL in 2012, but he was solid in coverage, surrendering completions on just 55 percent of the 113 passes he faced.

“I think we’re closer than people may think,” Smith said. “We just didn’t make enough plays. The plays were there to be made.”

Mixed numbers

Although the Dolphins’ pass-defense numbers were brutal (they gave up 248 yards per game, sixth-most in the league), Pro Football Focus’ rating system indicates they actually were a better-than-average coverage team.

Their top-line stats were skewed in part by how often teams threw against the Dolphins (37.5 times per game — sixth-most in the league). But the team was solid in yards allowed per pass attempt (7.0), completion percentage (58.8) and third-down defense (opposing teams converted just 36.6 percent of the time).

Still, the Dolphins didn’t have a player ranked in the top half of the 113 NFL corners who were on the field for at least 25percent of their team’s defensive snaps. Pro Football Focus gave Carroll (ranked 68th), Smith (75th) and Jimmy Wilson (86th) below-average grades in 2012.

Smith’s fate could be tied to what the Dolphins decide to do with Richard Marshall and Dimitri Patterson in 2013, who together would consume $10 million of the franchise’s salary cap should both return. Marshall’s $5.8 million cap number in 2013 would be the third-biggest on the team, behind just Karlos Dansby ($8.6 million) and Paul Soliai ($7.4 million).

New option?

Patterson is probably the team’s most intriguing option currently under contract for 2013. He started the last two games after the team scooped him off the waiver wire, and performed well. Quarterbacks completed just 27.3 percent of the passes thrown in his coverage area, for a rating of 69.9.

It’s hard to give a true evaluation of Marshall, because he injured his back in the second game of the season and played injured for the next couple of weeks before ultimately having surgery to repair two ruptured disks.

That shuffled the deck.

The Dolphins would have preferred Carroll to be their nickel back all year, but when Marshall went down, he got inserted into the starting lineup, and Wilson slid into the sub package. Neither seemed entirely comfortable in their new positions, particularly Wilson, who allowed 65percent of passes thrown in his direction to be completed. Furthermore, Carroll missed the final two weeks of the season with a knee injury, although he said he could have played Sunday at New England.

‘Critical’ offseason

When asked Monday if the Dolphins can win consistently with their current corners, Philbin dodged the issue a bit, saying the team’s defensive shortcomings were not isolated to the secondary.

Still, it wasn’t exactly a rousing endorsement for the group, which makes Carroll — entering the final year of his rookie contract — smart for viewing this as a make-or-break offseason.

“I think it’s critical,” he said. “I’m just trying to improve on what I can improve on. I can’t control anything else that doesn’t involve me.”