Lock in the experts; they only pretend to work (9)
I believe the answer is:
actresses
'they only pretend to work' is the definition.
(I've seen this before)
'lock in the experts' is the wordplay.
'lock' becomes 'tress' (both can mean a piece of hair).
'in the' indicates putting letters inside.
'experts' becomes 'aces' (ace is a kind of expert).
'tress' placed within 'aces' is 'ACTRESSES'.
(Other definitions for actresses that I've seen before include "Starlets" , "Stage performers" , "Female impersonators" , "Female performers" , "Girls in play" .)