His stable is unstable, it's found (9)
I believe the answer is:
establish
'found' is the definition.
(found can mean to set up or establish)
'his stable is unstable' is the wordplay.
'is unstable' indicates anagramming the letters.
'his'+'stable'='hisstable'
'hisstable' with letters rearranged gives 'ESTABLISH'.
'it's' is the link.
(Other definitions for establish that I've seen before include "Set up or found" , "Set up or settle firmly in place" , "form" , "Create - lodge" , "Verify" .)