An old venturer's dog? (5)

I believe the answer is:

rover

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'dog?' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for rover that I've seen before include "pirate ship" , "Car - dog" , "Vehicle driven remotely over extraterrestrial terrain" , "rambler" , "Person who wanders - a good name for dog" .)

I've seen this clue in the Evening Standard.

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