Old sea-dog? (5)

I believe the answer is:

rover

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'dog?' is the definition.
(Rover is a common name for a pet dog)

I can't explain the remainder of the clue.

(Other definitions for rover that I've seen before include "pirate ship" , "rambler" , "Pirate; dog's name" , "Itinerant person" , "Person given to wandering" .)

I've seen this clue in the Evening Standard.

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