Had effect around hard marine rock again and again? (9)
I believe the answer is:
threefold
'again and again?' is the definition.
Both the definition and answer are adverbs. Maybe they are linked in a way I don't understand?
'had effect around hard marine rock' is the wordplay.
'had effect' becomes 'told' (I've seen this in another clue).
'around' is an insertion indicator.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'marine rock' becomes 'reef' (I have seen 'Submerged rock ' mean 'reef' so perhaps 'rock' could also mean 'reef'. I am not sure about the 'marine' bit.).
'h'+'reef'='hreef'
'told' going around 'hreef' is 'THREEFOLD'.
Can you help me to learn more?
(Other definitions for threefold that I've seen before include "Triple" , "in several parts" .)