As the third day of the NFL free agent frenzy unfolded Thursday, defensive backs became the most conspicuous targets for teams hoping to tame the league's prolific, pass-happy offenses.

The San Francisco 49ers were one of the most active, and they should be attractive to several veteran stars with the goal of earning a Super Bowl ring before their career ends.

After losing Pro Bowl safety Dashon Goldson to the Tampa Bay Buccaneers Wednesday, the 49ers scheduled or desired talks with four former All-Pro defensive backs -- Charles Woodson, Nnambi Asomugha, Ed Reed and Darrelle Revis.

The 49ers reportedly scheduled talks with Woodson, Asomugha and safety Louis Delmas, but Reed was in Houston Thursday and Revis remains in a tug-of-war between the New York Jets and Tampa Bay.

Meantime, other teams were busy grabbing pass defenders.

Cornerback Sean Smith (last with Miami Dolphins) signed a three-year deal Thursday worth up to $18 million, including $11 million in guarantees. Smith, 25, had 12 passes defensed, two interceptions and three forced fumbles with the Miami Dolphins last season.

Also, cornerback Dominique Rodgers-Cromartie (Philadelphia Eagles) joined the Denver Broncos, safety LaRon Landry (New York Jets) signed with the Indianapolis Colts and cornerback Derek Cox (Jacksonville Jaguars) agreed with the San Diego Chargers, while cornerback Cary Williams (Baltimore Ravens) and safety Kenny Phillips (New York Giants) moved to Philadelphia.

Cox's deal is reportedly for $25 million, including $10.25 million guaranteed and a $5.2 million signing bonus. Landry received a deal worth $24 million over four years and Rodgers-Cromartie will earn $4 million for one year.

As attractive as the remaining field of available veteran defensive backs is, teams must weigh their value and career length against an April draft that may contain the deepest pool of talent in memory at the defensive back positions.

According to ratings by NFLDraftScout.com, there are 14 college cornerbacks and safeties who could be selected in the first or second round. Overall, NFLDraftScout.com lists 33 cornerbacks and 20 safeties as worthy of being drafted.

But teams are still showing respect for the veterans.

Reed traveled to Houston to visit with the Texans and general manager Rick Smith, who was on board franchise owner Bob McNair's private jet. Reed, who 35 before the start of the 2013 season, said in February before the Super Bowl that he has much more football left in his body.

Reed was a college teammate and remains good friends with wide receiver Andre Johnson. Johnson was expected to be a part of the Texans' courtship. Baltimore hopes to re-sign Reed, but the Ravens don't have the salary cap space to push all of their chips into Reed's basket.

Meanwhile, in San Francisco -- well, technically Santa Clara, where the team office and under-construction stadium sit -- the 49ers were set to entertain two All-Pros who were originally drafted and starred with the Oakland Raiders -- Woodson and Asomugha.

According to his agent, Carl Poston, Woodson flew into the Bay Area Wednesday night and was to talk to 49ers executives Thursday.

"He's going on a visit there and then we'll see what happens," said Poston. "He wants to go to a contender; he wants to get another Super Bowl ring."

The Green Bay Packers released the 36-year-old Woodson last month. He played in just nine games last year, compiling 50 tackles, making one interception and recording one-and-a-half sacks.

"Charles believes he can play several more years and bring some leadership to a team," Poston said. "He's like a coach on the field."

Woodson won the Heisman Trophy in 1997 while at the University of Michigan, the same school that produced 49ers head coach Jim Harbaugh.

Asomugha, 31-year-old former star at Cal-Berkeley, was released last week by the Philadelphia Eagles after struggling the past two seasons. He is guaranteed $4 million from the Eagles regardless of his next team or contract. The 11-year veteran was regarded as one of the league's top cornerbacks while playing for the Oakland Raiders.

The 49ers were interested in Asomugha when he was a free agent two years ago, but never scheduled a visit. Asomugha may not find the open market to his liking this time. He's definitely not going to touch the $60 million max value deal he scored from the Eagles in 2011.

Still, if the 49ers dawdle in considering multiple prospects, Asomugha has other potential suitors, including the New Orleans Saints, where defensive coordinator Rob Ryan knows Asomugha well from the days he coached the corner during his best years with the Raiders. When Ryan was with the Dallas Cowboys, he tried to get Asomugha before the Eagles landed him.

Other interested teams include the Arizona Cardinals, Texans and Broncos.

The Eagles didn't waste much time replacing Asomaghu and completing an overhaul of their secondary with two more signings Thursday. In total, they brought in two new starters at cornerback and a fresh pair of safeties in the first 48 hours of free agency.

Safety Phillips signed a one-year deal and will pair with Patrick Chung in the defensive backfield and cornerback Cary Williams, whose three-year, $17 million deal puts him in line to start alongside newcomer Bradley Fletcher. Fletcher signed a two-year deal on Tuesday.

All four additions are physical, aggressive players, a drastic change from the 2012 secondary.

The Colts confirmed the Landry signing, which was foreshadowed by general manager Ryan Grigson in February, when he stressed the importance of experience and leadership at the position.

Numerous early reports indicated the 49ers were interested in Revis, and vice versa, but he appears to be entangled in difficult negotiations between the Jets and Buccaneers.

According to a Yahoo! Sports report, the Buccaneers are hedging on dealing the 13th overall to land Revis, and may be angling to pay a first-rounder in 2014.

Sources told Yahoo that new Jets general manager John Idzik is willing to hold onto the cornerback until the April draft or longer, despite the fact that Revis will earn a $1 million roster bonus if he's still with the team on Saturday.

"One million is a pittance in the big picture when you're talking about a player of Revis' stature and the compensation he could bring," a league source told Yahoo! Sports on Wednesday. "Don't be foolish with something like that."

Meanwhile in Indianapolis, Grigson was "ecstatic" over signing Landry.

"We feel LaRon is an absolute game changer and a true impact player," he said. "We're talking about a 220-pound safety that runs 4.3 and plays to that speed. His approach to the game and his style of play are lights out and embody the culture we're building on the defense and this team in general."

Landry, 6-0, 220 pounds, played for the Jets last season and the Washington Redskins from 2007-11. He has started 79 of his previous 80 games. He has six interceptions, 10 forced fumbles, 5.5 sacks and 535 tackles.