“I want to win a national championship. That would, to me, be more important than being a head coach . . . because I have a lot of input into what goes on,” Virginia Tech defensive coordinator Bud Foster said. (Geoff Burke/GETTY IMAGES)

There are two ways of knowing that Virginia Tech defensive coordinator Bud Foster has a unit capable of being the nation’s best.

He yells a lot more at his players and speaks to Coach Frank Beamer a lot less.

The first is simple. There’s a fun-loving version of Foster who is prone to doing cartwheels upon hearing good news from a recruit and enjoys “wake surfing” when he’s relaxing at his Claytor Lake home near Blacksburg. But Foster says his “patience wears a little thinner, especially with high expectations” when football season rolls around.

It’s an offshoot of the mind-set he adopted on his way to becoming one of the top defensive minds in college football: “About the time you start feeling good about yourself is when you’re gonna get your tail knocked off.”

His relationship with Beamer is more complicated, considering the coach is the only boss Foster has ever known.

He played linebacker for Beamer at Murray State, and when Beamer became head coach there in 1981 he hired Foster as a graduate assistant. They’ve been together since, turning Virginia Tech into a national power along the way.

The odd thing is, part of the way Foster measures his success is how often Beamer is around the defense during a game week. If Beamer does more than simply watch drills during Tuesday’s practice or go over the game plan the day of a game, there’s something wrong.

“My job is to keep him out of that room when it’s all said and done,” Foster said one day last month, motioning toward the defensive meeting room in Virginia Tech’s football office. “He’s a good football man, a good football mind, a defensive guy. If he ever comes and offers any help, I’d be happy to take it.

“But he trusts us and it’s a good thing.”

It should be the case once again in 2012, when Virginia Tech will rely on a defense that will be the driving force if the Hokies are to finally fill their empty national championship trophy case this season. The Hokies return nine starters from a unit that, despite a wave of injuries, still finished ranked 10th in the country in total defense last season.

The offense has talented quarterback Logan Thomas back from a record-setting first year under center, with veteran weapons like wide receivers Marcus Davis, D.J. Coles and Dyrell Roberts. But the Hokies are also breaking in a tweaked up-tempo spread scheme, a new stable of running backs and four offensive linemen.

Foster sees similarities between this Virginia Tech defense and the ones that finished ranked No. 1 in the country in total defense in 2005 and 2006. It starts with a deep defensive line that returns a national-best 40 sacks and features up to nine players who could be shuffled into the lineup during a game.

Publicly, Foster is quick to point out potential stumbling blocks, such as a secondary that has talent but lacks veteran reinforcements should injury strike.

“We took strides last year,” he said recently. “I want to be a dominating defense. Can we be that? We’ll find out.”

On the opening night of training camp, however, Foster laid out the sort of season-long goals only elite defenses can aspire to. One, in particular, stuck out to his players: 13 touchdowns.

That’s how many the 2006 team gave up, one less than what defending BCS national champion Alabama allowed last season.

“We feel like we have the talent on our side of the ball to be the best defense that’s ever been through here,” cornerback Antone Exum said at Virginia Tech’s media day earlier this month.

The proliferation of spread offenses around the country, and at ACC rivals Clemson and North Carolina, make that task harder. If Virginia Tech’s defense does hold up its end of the bargain this season, it could be a late-career boon for its defensive coordinator.

Foster, 53, is not “naive enough to know my window of opportunity as a head coach is getting smaller and smaller as I grow older in age.” He has been selective in hopes of receiving an opportunity at a Bowl Championship Series school, and is aware that he may only get one shot.

Foster could have left Blacksburg any number of times. After he won the Frank Broyles Award as the nation’s top assistant coach in 2006, he declined overtures from South Carolina’s Steve Spurrier, Georgia’s Mark Richt, Florida’s Urban Meyer and Florida State’s Jimbo Fisher to become their defensive coordinator.

To ensure Foster would only leave Virginia Tech for a head coaching position, Virginia Tech guaranteed him an $800,000 annuity payment if he’s still coaching with the Hokies through the 2014 football season. One of the highest-paid assistants in the country, he earned a base salary of $471,762 in 2011.

“I could run a good football program. There’s no doubt about that,” Foster said.

Instead, he is funneling any built-up frustration into Virginia Tech and a defense that could very well keep Beamer away from Foster’s meeting room once and for all.

“I want to win a national championship. That would, to me, be more important than being a head coach . . . because I have a lot of input into what goes on,” Foster said. “You want to go back. Whatever that feeling is, there’s nothing like it in sports. You’re always wanting to get that back again, but it’s fleeting. You forget real quick.”