Secure unstable salvage (6)
I believe the answer is:
rescue
'salvage' is the definition.
(I've seen this before)
'secure unstable' is the wordplay.
'unstable' is an anagram indicator.
'secure' is an anagram of 'RESCUE'.
(Other definitions for rescue that I've seen before include "Deliver from danger" , "Retrieve" , "Save from harm" , "Secure (anag) - deliverance" , "Help out of difficulty, save" .)