Search for doctor at border (6)
I believe the answer is:
dredge
'search' is the definition.
(dredging is a kind of searching)
'doctor at border' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'at' is a charade indicator (letters next to each other).
'border' becomes 'edge' (synonyms).
'dr'+'edge'='DREDGE'
'for' is the link.
(Other definitions for dredge that I've seen before include "Drag up" , "(Of harbour or river) make deeper" , "Scoop up mud and silt from harbour bottom" , "Dig up mud from river or canal bed" , "Clean out the bed of a river or harbour" .)