Secure way of working with gold (4)
I believe the answer is:
moor
'secure' is the definition.
(mooring is a kind of securing)
'way of working with gold' is the wordplay.
'way of working' becomes 'mo' (I've seen this in other clues).
'with' is a charade indicator (letters next to each other).
'gold' becomes 'or' ('or' is the heraldic name for gold).
'mo'+'or'='MOOR'
(Other definitions for moor that I've seen before include "Secure boat with ropes" , "Room for Moroccan Muslim" , "Tract of open upland" , "Othello, perhaps" , "Heath - a North African Muslim" .)