Essentially, tall locals patrol Maze prison (8)
I believe the answer is:
alcatraz
'prison' is the definition.
(former US prison)
I don't understand how the remainder of the clue works.
(Other definitions for alcatraz that I've seen before include "old US jail" , "US island of a former maximum-security prison" , "Once-notorious prison in San Francisco Bay" , "Old Calif. offshore prison" , "Once dreaded prison in San Francisco Bay" .)