Two of TV’s high-profile crime franchises face a huge challenge next season: They have to replace their male leads. In the case of Law & Order: Special Victims Unit, Christopher Meloni made the decision to walk away from the NBC drama after 12 seasons, despite a ”generous” salary offer by the Peacock to play Detective Stabler for the 2011-12 season. (His costar Mariska Hargitay recently closed a deal to stay put.) Meanwhile, CBS opted to say goodbye to CSI‘s Laurence Fishburne, who joined the show in 2008, replacing William Petersen. Though the actor was a headline-making hire, his portrayal of Dr. Raymond Langston was not enough to get fans to forget Petersen’s Gil Grissom. This season the drama slipped to No. 35 among adults 18-49. Since CSI remains the most successful drama in the franchise (CSI: NY was the least watched, with 10.9 million viewers, while the mothership lured 13.6 million), CBS, like NBC with SVU, is expected to hire a new star for CSI‘s season 12. ”You are looking at shows that have been on the air a number of years, at which point sometimes change is a good thing,” says Bill Carroll, director of programming for Katz Media Group. Just in case the networks are stumped, we have casting suggestions: Promote Ice-T to lead detective on SVU, and hire Terry O’Quinn — a.k.a. John Locke from Lost — to go behind the yellow tape on CSI.