Mike Zimmer was in a relaxed mood in March as he sat with reporters at the NFL owners meeting in Florida. The conversation ping-ponged between topics, eventually turning to his improved defense.

Zimmer didn't take the bait when asked if his defense has top-5 potential.

"I don't know," he said. "I don't think we're very good, to be honest with you."

His chuckle provided a hint that this was merely a case of Zim being Zim.

Never let them relax or feel content. Keep pushing, keep demanding. Being good is not good enough.

"We can be a lot better," he said.

Zimmer arrived at Winter Park with a reputation as "The Fixer," a moniker that seems appropriate entering his third season.

The about-face by his defense has been a quick fix, but Zimmer's blueprint looks sustainable for the long haul, as much as anything in today's NFL can be viewed through that lens.

The recent re-signing of safety Harrison Smith served as a $51 million symbol of a plan implemented by Zimmer and General Manager Rick Spielman in aspiring to build a championship-caliber defense.

The marriage of Zimmer's scheme with the development of a core of young, promising talent has altered the organization's entire identity.

This is not only Adrian Peterson's team anymore. This is a defensive-minded operation built around a nucleus of players who are either entering their prime years or well on their way to establishing their foothold in the league.

The Zimmer/Spielman plan revolves around a core of players who are on their first or second contracts: Smith, Anthony Barr, Linval Joseph, Everson Griffen, Xavier Rhodes, Sharrif Floyd, Eric Kendricks and Danielle Hunter.

With the exception of Hunter, all of those players range in age from 24 to 28 — the sweet spot in an NFL career.

Hunter, who turns 22 in October, was the youngest player in the NFL last season.

"There's a whole lot of energy on this side," said Kendricks, who became the first rookie to lead the team in tackles (105) since the 1961 season. "We all have the same mentality, the same mind-set. We push each other to be better every day."

The defense doesn't feature a superstar in the same stratosphere as J.J. Watt or Von Miller or Luke Kuechly. The Vikings have assembled a collection of good-to-very-good players — Pro Bowl caliber in a few cases — who fit Zimmer's scheme and personality.

What's most encouraging is the nucleus has a chance to grow and develop together for the foreseeable future.

Finding the right balance between youth and experience remains a complicated puzzle for NFL decisionmakers. Being too young often results in growing pains. Being too old brings risk of sharp decline, or falling completely off the cliff.

The fluid nature of NFL rosters — with injuries, free agency and salary cap implications — makes long-term planning a delicate proposition.

But on paper at least, the Vikings are constructing their defense with a smart philosophy.

"That's kind of what I think we all have in mind," said Smith, a day after signing an extension that makes him the highest-paid safety in the league. "I'm obviously happy to be a part of it and the potential that we have. There's still a lot that we have to do. We can't just show up and be a good team."

That shouldn't be a problem with Zimmer, never one to tolerate complacency. But it's reasonable to feel optimistic about the way things are trending.

The Vikings finished dead last in the NFL in scoring defense the season before Zimmer's arrival. They were 11th his first season, fifth last season.

They also ranked among the best in third-down defense and red-zone defense last season.

Smith declined to go too far down the path of ranking the potential of the current defense compared to others he's coached.

"I know Zim wouldn't like that," he said.

Hunter didn't hold back.

"It can be the No. 1 defense," he said.

Their defensive core could become stronger, and deeper, if a few prospects become impact players. Specifically, we know little about 2015 first-round cornerback Trae Waynes or rookie second-round pick Mackensie Alexander.

Keeping a core intact, of course, often comes down to financial considerations. Those decisions fall on Spielman and salary cap guru Rob Brzezinski. The team faces looming contract decisions on Rhodes, Floyd and eventually Barr.

For now, their template for building and sustaining a top-notch defense makes sense.

Chip Scoggins chipscoggins@startribune.com