Police dog must have one name, right? (7)
I believe the answer is:
handler
'police dog must have one' is the definition.
(a police dog has a human handler)
'name right?' is the wordplay.
'name' becomes 'handle' (a handle is a name).
'right?' becomes 'r' (common abbreviation).
'handle'+'r'='HANDLER'
(Other definitions for handler that I've seen before include "One in charge of police dog" , "Person in charge of police dogs, boxers or spies" , "Boxer's trainer" , "Person in charge of dog etc" , "Boxer's second" .)