IRVING, Texas -- Dallas Cowboys owner/general manager Jerry Jones said he's been doing some of his best work in years, despite the fact that his team is 21-21 since Jason Garrett took over as coach in 2011.

The Cowboys have also missed the postseason the past three seasons.

"The facts are I really do think, the way things have rolled out, I'm getting to do some of the best work that I've done, relatively speaking in my career, over these last several years," Jones said Friday morning on KRLD-FM.

Since 1997, the Cowboys have posted a 133-133 mark with Jones as GM.

The Cowboys have struggled on defense this season, ranking 31st overall, last against the pass and 29th against the run. Last year, Jones fired defensive coordinator Rob Ryan, now with the New Orleans Saints, and hired 73-year-old Monte Kiffin. Jones expressed confidence in Kiffin earlier this week and isn't second-guessing the decision to hire him.

The Cowboys (5-5) have allowed opposing quarterbacks to throw for 400 or more yards an NFL-record four times, gave up a league-record 40 first downs to the Saints two weeks ago, and watched Detroit Lions receiver Calvin Johnson catch 14 passes for 329 yards against them Oct. 27.

Injuries have hurt the unit, with defensive end DeMarcus Ware (thigh injury) missing three games and cornerback Morris Claiborne (two games), safety J.J. Wilcox (three games) and defensive tackle Jason Hatcher (one game) also having been lost to injuries.

Jones also made the move to have Garrett no longer call the offensive plays. Instead, offensive coordinator/offensive line coach Bill Callahan is doing it.

It's been met with mixed results.

The Cowboys had a franchise-low nine rushing attempts in a Nov. 3 victory over the Minnesota Vikings, dealt with injuries to wide receiver Miles Austin and lost starting guard Brian Waters to a season-ending triceps injury.

But Jones is confident the return of several players from injuries will help over the final six weeks of the season and push the team into the playoffs.

Jones noted he plans on serving as GM for another 10 to 15 years. He has told the players he'd rather be with them than do anything else.