Mac plunged over the steep edge while out walking with owner Margaret Sills along a coastal path on the island.
But the collar caught on jutting rocks, breaking his fall.
"It saved his life," said Mrs Sills, "If he hadn't been wearing one he would have just free-fallen all the way and there's no way he could have survived."
Mac was taken to Riverbank Animal Hospital where he was treated for broken legs and a punctured lung.
Four days later surgeons fitted metal pins in two operations to keep his broken bones in place.
"He'll be in the plaster casts for six months so he can lead a true dog's life until then," said Mrs Stills.
"He can't really move so I've been helping him get outside on special ramps I made for him. He can barely support his own weight so I even have to support him when he goes to the toilet. He's really embarrassed I'm sure."
Mrs Sills, a former PA who has suffered four strokes and struggles to walk herself, said Mac's survival meant everything to her.
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