Rubbish prison, said dissenting voice (9)
I believe the answer is:
refusenik
'dissenting voice' is the definition.
(refusenik can mean someone against authority)
'rubbish prison said' is the wordplay.
I cannot really see how this works, but
'rubbish' could be 'refuse' (both can mean waste material) and 'refuse' is found within the answer.
This explanation may well be incorrect...
(Other definitions for refusenik that I've seen before include "Soviet dissident" , "who refuses to cooperate" , "Protester" .)