It's a mystery to me: dog locks

Last night, at the Ballard Market, I saw (and not only saw, but thought about) a locking dog-leash for the first time. I know people like their pooches, but I was a little baffled. Someone is going to snatch this St. Bernard? Will people actually steal something as troublesome as a dog?

For me, at least, the very dog-ness of a dog functions as a virtual lock. But I guess people really do steal dogs? And even if they don't, their owners love them enough that they want to make sure.
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