Prevent, say, those with no socks (5)
I believe the answer is:
avert
'prevent' is the definition.
(averting is a kind of preventing)
'say those with no socks' is the wordplay.
'say' becomes 'aver' ('aver' can be a synonym of 'say').
'with no' suggests deleting specific letters.
'socks' becomes 'hose' (I've seen this before).
'those' with 'hose' taken away is 't'.
'aver'+'t'='AVERT'
(Other definitions for avert that I've seen before include "use preventive measures" , "Prevent from occurring" , "Ward off, deflect" , "Turn aside, perhaps gaze" , "Turn away, prevent" .)