Fool going around Harden for valued possessions (6)
I believe the answer is:
assets
'valued possessions' is the definition.
(I've seen this before)
'fool going around harden' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'going around' indicates putting letters inside.
'harden' becomes 'set' (I've seen this before).
'ass' enclosing 'set' is 'ASSETS'.
'for' acts as a link.
(Other definitions for assets that I've seen before include "Resources or holdings ( 6)" , "Property owned by person or business" , "Useful or valuable possessions or qualities" , "worldly goods" , "Valuable property" .)