Mick Holt's no good as a security device expert (9)
I believe the answer is:
locksmith
'a security device expert' is the definition.
I can't judge whether this definition defines the answer.
'mick holt's no good' is the wordplay.
'no good' indicates anagramming the letters (no good can mean faulty or defective).
'mick'+'holts'='mickholts'
'mickholts' is an anagram of 'LOCKSMITH'.
'as' acts as a link.
Can you help me to learn more?
(Other definitions for locksmith that I've seen before include "Maker of security devices" , "opener" , "laughing stock" , "Security worker" , "Maker of secure fasteners" .)