That's right. They can sometimes slip down to the side of the body, but they don't get internal.
Some friends of ours breed German Shepherd Dogs (yeah, that's the correct name, not German Shepherd). Someone who had adopted one of their dogs lost the dog. It was later recovered by a rescue group who, once they learned that it was from a breeder, decided to save the dog from these "evil" people. Only trouble is that these are very respected breeders, and not the backyard type.
Someone in the group ratted them out, and it took a visit to the foster home with a cop and a chip scanner to get the dog back. Even though the dog was ecstatic to see the breeders, they couldn't have *proven* ownership without that chip. The cop made a show of asking if they wanted to press charges too.
Short version of the story, but there's two points here. The chip can help you, but only if the people who find the dog give a damn. We have all of our dogs chipped btw.