Guinea pigs should not wear collars because they can hurt their necks. You can; however, buy walking harnesses or regular harnesses for guinea pigs. Talk to your veterinarian Fairfield, TX about a harness. He can help you make sure you get the right size. You can probably take your guinea pig in for a check up with the harness on and get help making sure it fits correctly. As for ID tags, unless you can find one small enough, you may need to make your own type of ID tag just for the purpose of marking the harness or marking your guinea pig when he’s wearing the harness. Typical ID tags are too big for guinea pigs. Some owners have had their pedigree guinea pigs microchipped; however, some experts also discourage this because the chips and the needles used for the process are too big for guinea pigs. Click here to know more.