The San Francisco 49ers added veteran depth to their secondary Saturday by signing St. Louis Rams unrestricted free agent Craig Dahl to a three-year contract.This is not a flashy signing, but Dahl has the potential to help in multiple ways.Dahl, 27, has started 40 games for the Rams over the past four seasons, including all 16 in 2012. He's better against run than pass and has played quite a bit on special teams. His addition gives the 49ers improved depth at safety.