Shore up an exit and circulate (9)
I believe the answer is:
propagate
'circulate' is the definition.
(I know that circulate can be written as propagate)
'shore up an exit' is the wordplay.
'shore up' becomes 'prop' (I've seen this in another clue).
'an' becomes 'a'.
'exit' becomes 'gate' (I've seen this before).
'prop'+'a'+'gate'='PROPAGATE'
'and' acts as a link.
(Other definitions for propagate that I've seen before include "Advertise widely" , "widely spread" , "broadcast" , "Promote (an idea) widely" , "Produce more" .)