Make stronger check on police, perhaps (9)
I believe the answer is:
reinforce
'make stronger' is the definition.
(I've seen this before)
'check on police perhaps' is the wordplay.
'check' becomes 'rein' (both can mean to control or limit).
'on' is a charade indicator (letters next to each other).
'police perhaps' becomes 'force' (police is a kind of force).
'rein'+'force'='REINFORCE'
(Other definitions for reinforce that I've seen before include "Buttress" , "Give added strength to" , "increase support" , "Make stronger" , "give added support" .)