Every animal in this house has a chip. The poodles (two) were done by the breeders. The cats (two) were done by the adoption agencies. The greys (six) were done by me. Perry has two chips because the one put in by the breeder's vet is not easy to find. None of the other 10 chips has moved.
I have collars and tags on the dogs, but collars can come off and tags can be lost. The chip will ensure that the dog will be returned, and the process is far faster and more reliable than trying to read tattoos and track through the various agencies. My vet clinic is on a fairly busy corner and gets a lot of "found" dogs without tags: those with chips go straight back to their people; the others are picked up by Animal Services. As far as I can ascertain, the link to tumours is specious.