Try attaching the millimeter scanner (MMS) to your weapon.

The Millimeter Scanner (MMS) is a particularly effective attachment in 'Black Ops II.' When a player aims down the MMS, it pulsates every few seconds, revealing enemies behind cover or concealed by smoke within 25 meters, making it perfect for the game's Search and Destroy mode, where kills are worth five times those in Team Deathmatch mode. "When you're the last one alive and it's your chance to protect the bombsite, this attachment becomes powerful," says Wyatt. "Stay at a distance from the bombsite, but keep vision on any enemy attempting to defuse the bomb. This allows you to stay protected in cover, while keeping constant vision on the bombsite." It's essentially the best anti-camper weaponry since the mosquito.