As expected, the Detroit Lions have promoted Marcus Robertson from assistant secondary coach to secondary coach. Robertson replaces Tim Walton, who was hired this week as the St. Louis Rams' new defensive coordinator. Robertson joined the Lions last year as their assistant secondary coach. Before coming to Detroit, he coached for the Tennessee Titans from 2007-11. He was the Titans' assistant secondary coach from 2007-08 and was later promoted to secondary coach. He served that position from 2009-11. Before going into coaching, Robertson played in the NFL from 1991-2002. He was with the Titans franchise from 1991-2000, and he closed out his playing career with the Seattle Seahawks from 2001-02.