Mean to check over cause of exposure on beach (3,4)
I believe the answer is:
low tide
'cause of exposure on beach' is the definition.
(a beach is exposed when the tide is low)
'mean to check over' is the wordplay.
'mean' becomes 'low' (both can mean nasty or dishonourable).
'to' says to put letters next to each other.
'check' becomes 'edit' (edit can mean to check or emend).
'over' shows that the letters should be reversed in order.
'edit' backwards is 'tide'.
'low'+'tide'='LOW TIDE'
(Other definitions for low tide that I've seen before include "Farthest ebb of the waves" , "when recession at its most acute?" , "Condition of sea at its least high level" .)