ARLINGTON, Texas --To understand where veterans like Kevin Vickerson and Mitch Unrein are after Thursday's 27-3 preseason win over Dallas, one must go back to where they and the Broncos were four years ago.

In those days, the Broncos' defense was in disrepair. They allowed more yardage than anyone else in 2010, and its defensive line in the 3-4 alignment was panned by many pundits as the league's worst.

It was into that morass that Kevin Vickerson and Mitch Unrein arrived. Vickerson was on the 53-man roster, determined to prove his worth after being cast aside by Seattle. Unrein was on the practice squad, the Eastern Plains, hometown hero trying to latch on with the home-state team.

In the 4-12 season of 2010, the defensive line struggled. After coaching and administrative changes, a total overhaul was expected. But Vickerson and Unrein would become part of the solution: Vickerson as one of the first players John Fox chose to re-sign after becoming head coach, and Unrein by overcoming the odds to stick on the 53-man roster. Fox installed the 4-3 alignment he knew so well, and found Vickerson and Unrein to be good fits. They fortified the defensive tackle corps, and gradually, the Broncos' interior presence improved. The depth that was non-existent in 2010 soon became a strength.

Over the last four years, this weak spot became the defense's rock-solid core. And now it is so strong that the decisions at defensive tackle may be the most difficult on the roster.

Vickerson, Unrein, Marvin Austin and Sione Fua played all four quarters Thursday. Throughout the preseason, each has had moments where they were dominant. But there is not room for all.

"We have a lot of depth, and it's going to be some tough cuts," said Unrein.

Ends Derek Wolfe and Malik Jackson can swing inside in pass-rush situations. Austin was plucked off the scrap heap, his career and potential resuscitated by good health. First-rounder Sylvester Williams looks worthy of his lofty draft status. And Terrance "Pot Roast" Knighton is a gap-clogging force who is also a charismatic cult hero. Fua, a 2011 third-round pick of the Panthers, was dominant in the Aug. 17 shutout of the 49ers.

The inside depth is top-shelf, among the best in the league.

"It most definitely is. But that should be good. It should bring out the best in all of us," said Vickerson. "A lot of good plays made by our defensive line today."

Vickerson led the way with five tackles, including one in which he shed a blocker to make an ankle tackle of Dallas running back Phillip Tanner for a three-yard loss. Unrein added a third-quarter sack of Cowboys quarterback Dustin Vaughan that was just two feet away from being a safety.

And in the fourth quarter, the two proven veterans continued to pound away, work through double teams, stunt, twist and shake off blockers. It was the sort of extensive work that rotational defensive tackles rarely experience at this level, and it helped both settle into a groove.

"I haven't been able to start a game and play that many plays, pretty much, since college," said Unrein. "I think it helps when you get out there and you can play a lot of plays like that. You start getting kind of on a roll, an knowing what the offensive linemen like to do. You kind of get tips off their stance and things like that, and then you hear some of the calls, and things like that."

But familiarity doesn't breed security. Unrein knows this, as he's been on this sort of jagged, nervous edge at the conclusion of previous preseasons.

"I just came out here tonight and just tried to leave it all on the field," he said. "I know I can play in this league, and if it's for the Broncos, that would be great, but I feel like wherever it's at, hopefully I can contribute."

In the past few weeks, Unrein even got some work at defensive end -- "the more you can do, the better it is," he said -- to go along with history of contributions all over the field: multiple roles on special teams and offensive work as a short-yardage fullback.

Vickerson's goal this summer was not diversification, but recovery from the dislocated hip he suffered last Nov. 24 at New England. He wasn't cleared to practice until last month, and didn't take a game snap until last Saturday. But the hip passed the test of brief work then, and extensive duty Thursday.

"Every day it gets better," he said. "I'm going in a positive direction. We're not having any setbacks as far as soreness or anything like that. So that's all you can ask for.

"Well, that, and a roster spot. But like Unrein, Vickerson accepts the reality of the roster predicament.

"All I can do is what I can do and that's play. The rest is in their hands," he said. "I put it on film for them to see, to show the world what I can still do. After that, it's their decision."

Added Unrein: "It's in their hands, but I just wanted to put good tape out there for them to see. If it doesn't work out, then hopefully, get picked up by somebody else. But that's all you can really do, is have a job in this league, because it's fun playing in the NFL, and I don't want to see it end anytime soon."

Like many Broncos, they've proven, once again, that they are good enough to play in the NFL. But on a team blessed with talent, the task is more difficult -- both for them and those who make the decisions. Given where the Broncos were when Vickerson and Unrein arrived, it's a problem for which they are grateful. But that doesn't make these next two days any less painful.

"The team's not going to be the same after tonight," Unrein said. "It's hard."