They limit what one does with foils (6)
I believe the answer is:
fences
'foils' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe there's an association between them I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for fences that I've seen before include "Good ones make good neighbours, it's said" , "Engages in swordplay or processes stolen goods" , "Hedges and barriers" , "Dealers in stolen property" , "Avoids directly answering" .)