Fancy green dens for bears (9)
I believe the answer is:
engenders
'bears' is the definition.
(both can mean creates or gives rise to)
'fancy green dens' is the wordplay.
'fancy' is an anagram indicator.
'green'+'dens'='greendens'
'greendens' anagrammed gives 'ENGENDERS'.
'for' acts as a link.
(Other definitions for engenders that I've seen before include "Leads to" , "Gives rise to, causes" , "Brings forth, generates" , "Produces, causes" .)