After restraint certain to get cover again (8)
I believe the answer is:
reinsure
'cover again' is the definition.
('insure' can be a synonym for 'cover' so perhaps 'reinsure' is OK for 'cover again')
'after restraint certain' is the wordplay.
'after' means one lot of letters go next to another.
'restraint' becomes 'rein' (I've seen this before).
'certain' becomes 'sure' (similar in meaning).
'rein' put next to 'sure' is 'REINSURE'.
'to get' acts as a link.
(Other definitions for reinsure that I've seen before include "Take out another policy" , "recover?" , "Cover again" , "Pass on a risk of having to pay compensation" .)