The Razorbacks coach has reason to believe that might change in his fourth season.
Arkansas, which ranked last in the Southeastern Conference in total defense in 2009, jumped to fifth last season behind a talented and deep defensive front.
Seven starters return on defense this season for the Razorbacks, who believe they are on the way to becoming one of the top defenses in the SEC.
If that happens, Arkansas could reach its goal of contending for its first SEC championship and a return trip to a BCS bowl game.
"We have to go prove it, but I'm very encouraged coming in," Petrino said. "We took a huge step from Year 2 to Year 3 defensively. We just need to do that again."
The Razorbacks made a dramatic jump in offensive production in Petrino's second season in 2009, improving from 21.9 points per game to 36.
However, the team's defense fell from 72nd in the country to 89th allowing more than 400 yards per game.
Arkansas junior D.D. Jones played in 12 games as a freshman that season, including a 52-41 home loss to Georgia during which the Bulldogs gained 530 yards.
"When I first got here, it was tough," Jones said. "Our defense just wasn't that good, but we kept working to make the best of everything."
That work and experience paid off last season for the Razorbacks, who jumped to 36th in total defense and lowered their average yards allowed to 348 per game.
Arkansas finished second in the SEC with 37 sacks, led by seven from defensive end Jake Bequette.
Bequette skipped the NFL draft after last season to return for his senior year, and his past performance along with other veterans such as Jones, junior Tenarius Wright and senior Zach Stadther has Razorbacks linebackers coach Reggie Johnson eager for the season.
"We're excited because of the experience we have coming back, the front guys, the big bodies that can move," Johnson said. "There's a big upside, so the excitement level for me and the defensive coaching staff is huge."
Johnson is far from the only one at Arkansas sharing in the excitement.
"We can be great, the top defense in the nation," Jones said. "As long as we work hard, there's no doubt we can be the best defense there is. Now that the opportunity is here, we've got to make the best out of it again and let the world know what we're about."
Senior safety Tramain Thomas and fellow senior middle linebacker Jerry Franklin are among the returning starters, and both have seen action since their freshmen seasons Petrino's first.
Thomas was selected second-team All-SEC last season and had a career-high 83 tackles.
"The limit for us is through the roof," Thomas said. "I could have said that last season, but it wouldn't have been an honest response. We have the pieces, the guys, the coaches to do it now ... Through the roof."
Arkansas was second in the SEC in total offense last season, averaging 482.5 yards, but the two biggest contributors are gone.
Their absences could put additional pressure on the Razorbacks' defense as the team breaks in either junior Tyler Wilson or sophomore Brandon Mitchell at quarterback.
Franklin, who has led Arkansas in tackles in each of his three seasons and had 100 stops last season, believes the defense is ready for the challenge.
"We all believe we can be a dominant defense," Franklin said. "We believe we can go out and win a game, even when the offense isn't having a great game."