Genuine peacekeepers spread around one unoccupied garrison (9)
I believe the answer is:
unfeigned
'genuine' is the definition.
(I've seen this before)
'peacekeepers spread around one unoccupied garrison' is the wordplay.
'peacekeepers' becomes 'un'.
'spread around one unoccupied garrison' becomes 'feigned' (I can't explain this - if you can you should give a lot more credence to this answer).
'un'+'feigned'='UNFEIGNED'
Can you help me to learn more?
(Other definitions for unfeigned that I've seen before include "Sincerely felt or expressed" , "Genuine, not faked or put on" .)