Destroy a method for secession (9)
I believe the answer is:
breakaway
'for secession' is the definition.
(breakaway is a kind of secession)
'destroy a method' is the wordplay.
'destroy' becomes 'break' (breaking is a kind of destroying).
'method' becomes 'way' (way of doing something).
'break'+'a'+'way'='BREAKAWAY'
(Other definitions for breakaway that I've seen before include "secession" , "Escape" .)