So now cornerback Carlos Rogers joins secondary mates Donte Whitner and Tarrel Brown in the free agency pool.With the 49ers' announcement Monday that Rogers would be released, San Francisco now enters the free-agent signing period with 75 percent of its starting secondary (from the 2013 opener) on the market. If they get strong offers from other teams, the cornerback tandem of Rogers and Brown could be lost, as could starting safety Whitner.But as Bill Williamson of ESPN.com noted Tuesday, the loss of Whitner would be the biggest blow. Because of Whitner's strong play – and the shortage of good safeties on the free-agent market this season – it's important for the 49ers to re-sign him, wrote Williamson.In scanning the list of available free agents, Williamson writes that possible options to replace Whitner are ex-Raider Mike Mitchell of the Panthers, Malcolm Jenkins of the Saints and James Ihedgbo of the Ravens. In-house options would be C.J. Spillman and Craig Dahl. Though re-signing Whitner will be expensive, not re-signing him might be more costly to the 49ers' defense in 2014."The free-agent market is thin, and, in my opinion, signing Whitner is, by far, the best...