RENTON, Wash. -- When the Seattle Seahawks spent four draft picks on their secondary this spring, the message seemed to be clear. Pete Carroll, John Schneider & Co. were preparing the defense for a period of transition.

But with safety Kam Chancellor agreeing to a three-year, $36 million contract extension, the plan now appears to be different. The Seahawks believe their core players on defense and the Legion of Boom have a lot of good football left. Other than strongside linebacker, which is a part-time position, the entire starting defense is now under contract through the 2018 season.

Two years ago, Chancellor felt that he was underpaid and held out through the first two games of the regular season. It's perhaps the only blemish on a stellar seven-year career. Last year, he put the contract issues behind him and played at a high level. During one November night at Gillette Stadium, Chancellor matched up with New England Patriots tight end Rob Gronkowski on a game-deciding play and forced an incomplete pass.

In the locker room after the Seahawks' win, cornerback Richard Sherman spoke to what Chancellor means to the defense.

"There's no quantifying his impact," Sherman said. "There were run game fits. There were adjustments that he made on the fly. There were things where he got us in the right formation and got our line adjusted and things that you can't measure and a lot of times won't show up on film and won't show up on the stat sheet."

Chancellor is the leader of the Seahawks' defense. Carroll's coverage schemes are not complicated, but continuity has helped greatly over the years. This will be the seventh season that Chancellor, Earl Thomas and Sherman will be lining up together.

"We are like a machine, and if that one bolt is missing or that one part of the machine is missing, then it just doesn't function properly," Chancellor said Monday. "When we are all on the field, we are just like a dominant force, so having us all together is the best we can do and that's the best we can play with everyone up there."

In the past two years, when Chancellor has been on the field, opposing quarterbacks have posted a QBR of 48.6, according to ESPN Stats & Information. Without him, that number has been 70.3.

Until the details of the contract are released, it's tough to tell what kind of risk the Seahawks are taking on. Chancellor is 29 and plays the game with a punishing violence. He admitted Monday that he's not the same guy he was when he first came into the league.

"I'm not the same rookie I was seven years ago," Chancellor said. "It's a lot different. Everything is going to change. It won't stay the same forever. So it's going to change here and there."

But the Seahawks have put themselves in a good spot. Chancellor can lead the veteran defense for the next couple of years as the team attempts to get its hands on another Lombardi trophy.

And when the transition finally does take place, Chancellor can be the respected voice that the young players lean on.

"I love this team," Chancellor said. "They gave me the first opportunity and the only opportunity, and I would love to retire here."