If your cat is wandering and you don't want it to, keep it inside. House cats live longer, healthier lives, and are perfectly happy living safely in their homes as long as they have sufficient stimulation.
If you are not willing to keep your cat inside, put a tag on a cat-safe breakaway collar. Cats are naturally going to get into tight areas, and a tag hanging from a non-breakaway collar will result in a trapped, and possibly dead, cat. Collars approved for cats are made with clips that will pull apart with sufficient force, allowing the cat to pull itself free easily if the collar or tag become stuck somewhere. The cat will no longer have an ID tag at this point, so an implanted ID chip is a highly recommended backup to identify the pet if picked up by another individual or animal control.
Do not turn your cat loose while wearing a harness. Ever. The same hazards to a caught collar will apply to a caught harness, and while cats can often figure out how to twist their way out of a harness, the cat may be stuck in a position where it is unable to do so, or may not be able to figure it out. A harness is meant for supervised time on a leash only; a cat should never wear it while not being supervised. It is designed to be difficult to escape from because it is designed to keep the cat under control while leashed.