Dig up doctor by the border (6)
I believe the answer is:
dredge
'dig up' is the definition.
(I've seen this in another clue)
'doctor by the border' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'by' means one lot of letters go next to another.
'the border' becomes 'edge' ('edge' can be a synonym of 'border').
'dr'+'edge'='DREDGE'
(Other definitions for dredge that I've seen before include "Clear (riverbed)" , "Search" , "dragnet" , "Drag up" , "Remove material from a channel or riverbed" .)