Guard criminal (5)
I believe the answer is:
fence
I believe this clue is a double definition.
'guard' is the first definition.
(I've seen this before)
'criminal' is the second definition.
(I've seen this before)
(Other definitions for fence that I've seen before include "With blade, fight" , "Obstacle to clear, in steeple-chasing" , "Guard" , "Barrier - engage in swordplay" , "Wooden or wire barrier" .)