Manage to fence in small wood (5)
I believe the answer is:
copse
'wood' is the definition.
(a copse is a small wood)
'manage to fence in small' is the wordplay.
'manage' becomes 'cope' (manage can mean to cope or do well).
'to fence in' means one lot of letters goes inside another (inserted letters are fenced in).
'small' becomes 's' (abbreviation - e.g. clothes size).
'cope' going around 's' is 'COPSE'.
(Other definitions for copse that I've seen before include "Scope for a small wood" , "Small group of trees" , "Coppice" , "Dense thicket of trees" , "Piece of woodland used for cutting" .)