Flap Copper if your dog was to get lost, are there any marks on it's body you can identify it with?
Toby has 2 white rings almost where his dew-claws used to be, and a little dent in his left ear flap from when my cousins dog bit him as a pup.
mickie has a patch of dark skin on her chest area visible only when you part the hair. and she has a "boob" with 2 nipples on it. (yea i know weird...)
Copper has a little patch of white hair on his left hind leg right by his knuckles, and a little teeny patch of white hair on his muzzle.
All dogs from a registered kennels in Canada will have a tat in their ear. All of my dogs also have a Home Again microchip
