Rover, not out, barking (5)
I believe the answer is:
nomad
'rover' is the definition.
(nomad is a kind of rover)
'not out barking' is the wordplay.
'out' means to remove the last letter.
'barking' becomes 'mad' (barking mad).
'not' with its final letter taken away is 'no'.
'no'+'mad'='NOMAD'
(Other definitions for nomad that I've seen before include "is one unsettled?" , "Traveller with no permanent home" , "one must move on" , "Unsettled type" , "Person always on the move" .)