A turn of phrase used, to the best of my knowledge, only by people originating from Scunthorpe, England.
Correct usage is in reference to something one possesses in such abundance that the amount surplus to requirements would form a sufficient road surface, if cemented to a dog. For instance, both you and your flatmate take advantage of a special offer on Cheesy Quavers at the local supermarket. A person from Scunthorpe might remark:
"Oooh. We've got enough Quavers here to cobble a dog"
Really, I have heard this used more than once by different people. However, I have never seen it done, and so I have doubts both about the practicality of Quavers as a road surface and about the suitability of a dog mounted road.