At the main menu, select "Options", and choose "Extras". Select the "Enter Code" 
option, then enter one of the following case-sensitive codes to activate the 
corresponding cheat function. Note: Enabling codes will prevent the game from 
being saved and trophies from being unlocked.

  Gold Hammer 
  Enter "HARDHITTER" as a code.
  Gamestop Wrecking Crew maps 
  Enter "MAPMAYHEM" as a code to unlock the Gamestop Wrecking Crew maps.