Prevent everyone going east of woodland (9)
I believe the answer is:
forestall
'prevent' is the definition.
(I know that prevent can be written as forestall)
'everyone going east of woodland' is the wordplay.
'everyone' becomes 'all' (all people).
'going east of' is a charade indicator (letters next to each other) (some letters go to the right of others).
'woodland' becomes 'forest' (synonyms).
'all' after 'forest' is 'FORESTALL'.
(Other definitions for forestall that I've seen before include "Avert" , "Thwart" , "Arrive first" , "Stop" , "Prevent by taking advance action" .)