SANTA CLARA — Nothing establishes a defense like a hard-hitting safety, roaming the deep middle and clocking any opponent who ventures into the area unaware.

As they prepare for Saturday's NFC divisional playoff game against the Green Bay Packers, the 49ers don't have one of those guys. They have two. Free safety Dashon Goldson and strong safety Donte Whitner, while overshadowed by the likes of tackle machine Patrick Willis and sack hoarder Aldon Smith, form a punishing one-two punch in the San Francisco secondary.

"The physical presence that those two guys bring at the back end, it's amazing," 49ers cornerback Tarell Brown said. "It helps this team, and it also brings an identity to this defense."

Brown should know. He not only has witnessed plenty of big hits by his safeties. He was on the receiving end of one of them, when Goldson missed the Giants' Hakeem Nicks and inadvertently plastered Brown on a pass late in the third quarter of last year's NFC championship game. Brown suffered a concussion.

More frequently, the 49ers safeties limit their damage to the opposition.

Goldson's victims include Tampa Bay's Mike Williams and Cleveland's Greg Little in 2011, and Arizona's Early Doucet in Week 8 of this season; some called the hit on Doucet, which separated the wide receiver from the ball (and very nearly his molars) the hardest of 2012.

Whitner had a memorable body slam of Dolphins running back Reggie Bush in Week 14, but the hit that defines his two-year stint with San Francisco occurred just shy of a year ago, in a home playoff game against New Orleans. The Saints took the opening kickoff and, as they so often do behind Drew Brees, marched methodically down the field. But on third-and-7 from just inside the 49ers' 8-yard line, running back Pierre Thomas caught a pass at the 5, headed for the end zone — and was obliterated by Whitner.

The safety's helmet-to-helmet hit knocked Thomas cold and dislodged the ball, which was recovered by Willis at the 2-yard line. The 49ers had established a brutal tone that would help carry them to victory.

Asked if his teammate's hit got the Niners fired up, Goldson answered: "Through the whole stadium, man. That was definitely a picker-upper for us in that whole game. Just set the tone and our mindsets throughout those playoffs, because a lot of guys, it was their first time in the postseason, and we wanted to go out there and make our presence felt."

The 49ers have had past enforcers at safety. Ronnie Lott was pretty much the gold standard in that regard, and Tim McDonald inspired some fear, too. Around the NFL currently, players like Arizona's Adrian Wilson, the Jets' LaRon Landry and Seattle's Earl Thomas are known for their rugged play and heavy shoulder pads.

But it's rare to have two such enforcers in one secondary.

"Where do you go?" Goldson wondered aloud. "Like, who do you throw the ball to across the middle? At some point you have to make up your mind and throw the ball across the field somehow, because not every team has outside routes all the time. Some gotta come across that middle. So it's like, who do you challenge?"

"It creates some dilemmas," Whitner said. "It makes the quarterback think about how he's gonna deliver the ball to the wide receivers. A lot of times when we play teams they don't bring guys near us, to where we could really lay a big hit on a guy. And if they do throw it in there, they make sure they throw it low, so that we don't get a good lick on. That's what Aaron Rodgers was doing last time we played 'em."

Rodgers, the Green Bay quarterback, is known for spreading his throws among many different receivers; last week he set a postseason record by completing passes to 10 different guys. Inevitably, some of those throws will make receivers vulnerable to big hits.

"Guys know, just because they watch film," Brown said. "I mean, if you're seeing guys coming across the middle getting tattooed every play, you would know, and those arms get a lot shorter when you're going across the middle."

Not that Whitner and Goldson are one-dimensional headhunters. Coach Jim Harbaugh stresses their fundamentally sound tackling. Whitner is solid in covering tight ends, and Goldson has 14 interceptions over the past four seasons. Both made the Pro Bowl this year, Goldson as a starter.

"Those two guys are tough guys," Rodgers said. "They're very good tacklers. They bring the pop when they get the chance, and they're both very athletic and instinctual players. Understand the coverages and timing, right concepts, and do a good job of being in the right spot in their defense, making plays. They're very opportunistic."

With all that said, the trait that 49ers fans probably admire most — and the one that keeps opposing receivers awake at night — is the ability of Whitner and Goldson to inflict bodily harm.

Cornerback Carlos Rogers played with some intimidating safeties in Washington, including Landry, Ryan Clark and the late Sean Taylor. Rogers sees a similar fear factor surrounding Goldson and Whitner, though, as he points out, neither is particularly big.

"You may not think they can bring it like that," Rogers said. "But them boys will knock you out."

(You can reach Staff Writer Phil Barber at 521-5263 or phil.barber@pressdemocrat.com.)