Barriers against crooks? (6)
I believe the answer is:
fences
'barriers' is the definition.
(fence is a kind of barrier)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for fences that I've seen before include "Good ones make good neighbours, they say" , "items for negotiation" , "Avoids directly answering" , "Uses a foil" , "Hedges and barriers" .)