Enjoy one's job looking after Charlie — secure and trouble-free (4,9)
I believe the answer is:
like clockwork
'trouble-free' is the definition.
(to work like clockwork is to work without problems)
'enjoy one's job looking after charlie secure' is the wordplay.
'enjoy' becomes 'like' (I've seen this before).
'one's job' becomes 'work' (a person's job or profession).
'looking after' indicates putting letters inside (inserted letters are guarded or looked after).
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'secure' becomes 'lock' (locking is a kind of securing).
'like'+'work'='likework'
'c'+'lock'='clock'
'likework' enclosing 'clock' is 'LIKE CLOCKWORK'.
'and' is the link.
(Other definitions for like clockwork that I've seen before include "Running superbly" , "Smoothly" , "With all parts functioning perfectly" , "Regularly" .)