Was a good dog (6)
I believe the answer is:
obeyed
'was a good dog' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for obeyed that I've seen before include "Did what one was told" , "Followed the rules" , "Carried out (a command)" , "Followed orders" , "Heeded" .)