Trevor, our new 3yr old Yorkie has been chipped twice..... both times by the puppy mill. The Chip is by Avid PetTrac. It is placed beneath the skin on the back between the shoulders. I the animal is picked up by the animal control, most can scan for the chip and then can contact you. I think all vets have a scanner also. Avid gives you a tag to go onto a collar or harness. We also have a tag we got from PetSmart that has his name and our phone number.
However as Ray said, keep them close and never alone. However not all of our fur kids like to hang around and can jump out or get away. If I were you I would keep a collar on your Lab with numbers and name and go to the vet and have him chipped.
FWIW
BC