"The Rock” (8)
I believe the answer is:
alcatraz
'the rock' is the definition.
(Alcatraz prison was nicknamed the Rock)
This is all the clue.
(Other definitions for alcatraz that I've seen before include "(Former prison) island in San Francisco Bay" , "Californian island" , "Once dreaded prison in San Francisco Bay" , "Old Calif. offshore prison" , "Notorious US prison" .)