Trees always succeeded hiding part of golf course (10)
I believe the answer is:
evergreens
'trees' is the definition.
(I have seen 'Certain trees' mean 'evergreens' so perhaps 'trees' could also mean 'evergreens')
'always succeeded hiding part of golf course' is the wordplay.
'always' becomes 'ever' (synonyms).
'succeeded' becomes 's' (genealogical abbreviation).
'hiding' means one lot of letters goes inside another.
'part of golf course' becomes 'green' (golf courses have greens).
'ever'+'s'='evers'
'evers' placed around 'green' is 'EVERGREENS'.
(Other definitions for evergreens that I've seen before include "Certain trees" , "perennial favourites" .)