Where have the elite cornerbacks gone? The stifling, shutdown, don't-throw-my-way defender has become a rare commodity in the National Football League.

Good corners? Sure. Those can be found, developed and taught. But the truly great ones, those with length, instincts, speed and reliable hands, those are much, much harder to find. Harder, in fact, than ever before.

That is why Tampa Bay gave up its first-round draft pick to the New York Jets to acquire Darrelle Revis in April, even though Revis is coming off a significant knee injury that usually requires a full year from which to return. And it is why Denver's Champ Bailey is still considered one of the league's best corners at age 35.

"A lot of people today are winning with 2s and 3s," Carolina coach Ron Rivera said. "Guys that are a true No. 1, like a Darrelle Revis, those guys are hard to find. When you find one, you've got to get him."

Even though Darrelle Revis is coming off knee surgery, the Buccaneers gave up a first-round draft pick to acquire him from the Jets. AP Photo/Chris O'Meara

But where have they gone? What do they look like? And why are they so hard to find? In a league in which the quarterbacks are playing better younger, the wide receivers are getting bigger and faster, and offenses are throwing the ball at record numbers, how can cornerbacks keep up? How, essentially, can they win?

This offseason I asked several NFL head coaches those questions, and there was a consensus that it is harder than ever to find truly elite cornerbacks.

"It's not easy," New York Giants coach Tom Coughlin said. "Not easy. Very, very critical, critical position for you if you're going to match up against these great athletes who keep coming at you at receiver."

Coughlin said that for years the Pro Bowl standard for cornerback was to be 5-foot-11, 187 pounds with 4.55 speed. That profile nearly fits Revis, who is 5-11, 198 pounds and reportedly ran a 4.39 40-yard dash at his pro day in 2007. The Jets were so enamored that they traded a first-, second- and fifth-round pick to Carolina to move up 11 spots and draft Revis 14th overall.

Revis Island thus was born.

The value of size is in the eye of the beholder. Denver coach John Fox said he prefers taller corners, such as Bailey, who is 6-foot, and the 6-2 Dominique Rodgers-Cromartie, whom the Broncos signed this offseason.

"There's a fine line whether you can break down and change direction if you're too high cut and too long," Fox said. "The ability to have a quick twitch, to be able to react quickly, and ball skills always help, because there are some guys [who] there's a reason they're on defense. They can't catch. … But if the quarterback knows you can't catch, he'll buzz one by your ear. If you have good vision and good ball skills, they'll think twice about doing that."

Which is why Seattle's Richard Sherman is feared. He has good hands and an innate ability to knock the ball away before a receiver can catch it. He is big and physical. And in just two seasons since the Seahawks picked him in the fifth round of the 2011 draft, Sherman has become the prototypical corner in today's NFL.

According to Pro Football Focus, quarterbacks threw at Sherman 87 times during the 980 regular-season snaps he took in 2012. Sherman allowed the passes to be completed only 47.1 percent of the time, one of the best percentages in the NFL last season. This offseason, the Seahawks added former Minnesota corner Antoine Winfield, who is stout against the run although not an elite cover corner.

The Seahawks should have one of the best cornerback rotations in the NFL, along with Denver and Kansas City. Atlanta overhauled its secondary this offseason, as did Philadelphia, which two years ago had arguably three No. 1 corners -- with disastrous results -- but now have a bunch of No. 2s and 3s.

Why are the good ones hard to find? Rivera traces the line back to college. In the same way college gave the NFL quarterbacks who could run the pistol and read option, college has given the NFL corners with bad technique, Rivera said.

"Look at the technique," Rivera said. "Why do they have them in these 45-degree stances? Why are they shuffling out? What happened to the true backpedal where you plant and break? Why are they always playing this coverage?

"You put tape on and you could pretty much guarantee this team is always playing this coverage. In our league, some teams don't play as much man. Some teams play more zone. If you grab a corner that has all the skill set but that's not what he's used to doing, now you have to redevelop him and reteach him and he's got to relearn. There's a lot of things that go into play about why it's taking time, or they're just not finding those guys yet."