Loose stones, any number forming barrier (6)
I believe the answer is:
screen
'barrier' is the definition.
(screen is a kind of barrier)
'loose stones any number' is the wordplay.
'loose stones' becomes 'scree'.
'any number' becomes 'n' (I've seen this in other clues).
'scree'+'n'='SCREEN'
'forming' is the link.
(Other definitions for screen that I've seen before include "Standing partition" , "Protective frame" , "Room partition; vet" , "Hide - show - partition" , "Surface on which to project pictures" .)