I'll admit I've always had a weakness for the depth argument; interestingly, this has parallels to cyborg-issues. A grandfather clock does not make you a cyborg; a brainport does. How about a smartphone? Is it close enough to the body yet? How about a pacemaker, an enhancement inside your body? How about a cassette walkman? Where do we draw the line? Because it doesn't always seem to be at the skin.
Interesting point in the Q&A: Just because you own something doesn't mean you get to do anything you want with it. They make the point about property-as-in-land; mine's always been guns, cars, and cameras.