Oaf falling short spies a refuge (5)
I believe the answer is:
oasis
'a refuge' is the definition.
(I know that oasis is a type of harbor)
'oaf falling short spies' is the wordplay.
'falling short' means to remove the last letter.
'spies' becomes 'SIS' (Secret Intelligence Service).
'oaf' with its final letter taken off is 'oa'.
'oa'+'sis'='OASIS'
(Other definitions for oasis that I've seen before include "Manchester band featuring the Gallagher brothers" , "Spring of fresh water in a desert" , "Fertile place like waterhole in desert" , "Place of peace" , "where palms grow" .)