CHICAGO -

The Chicago Bears have agreed to a five-year contract with former Oakland Raiders defensive end Lamarr Houston.

They also agreed to a two-year contract with former Pittsburgh Steelers and New York Giants safety Ryan Mundy and one-year deals with linebackers Jordan Senn and D.J. Williams as they try to shore up a defense that got shredded by injuries and ranked among the league's worst last season.

The Bears announced the moves on Tuesday.

Chicago is coming off a season in which it allowed a league-high 5.3 yards per carry -- half a yard more than any other team -- and tied Jacksonville for an NFL-worst 31 sacks.