Prevents arrests? (5)
I believe the answer is:
stops
This clue is a double definition.
'prevents' is the first definition.
(stopping is a kind of preventing)
'arrests?' is the second definition.
(arrest is a kind of stop)
(Other definitions for stops that I've seen before include "Ends" , "Checks" , "Halts" , "Prevents" , "Posts (anag.)" .)