Take care - only insiders can do this (4,3)
I believe the answer is:
look out
'take care' is the definition.
(I've seen this before)
'only insiders can do this' is the wordplay.
I cannot quite see how this works, but
'can' could be 'loo' (slang) and 'loo' is found in the answer.
'do' could be 'ut' (synonyms) and 'ut' is found within the answer.
The remaining letters 'ko' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for look out that I've seen before include "Be on your guard!" , "Beware!" , "A view of the future" , "makes one be careful!" , "as Wenceslas did" .)