Shielded dealer in stolen property, diamonds (6)
I believe the answer is:
fenced
'shielded' is the definition.
(protected by fencing)
'dealer in stolen property diamonds' is the wordplay.
'dealer in stolen property' becomes 'fence' (I've seen this before).
'diamonds' becomes 'd' (abbreviation for the card suit diamonds).
'fence'+'d'='FENCED'
(Other definitions for fenced that I've seen before include "Surrender or guarded with railings" , "Engaged in sword sport" , "Enclosed as with bushes" , "Recieved stolen goods" , "Fought with swords" .)