Road taken through South African frontier (6)
I believe the answer is:
border
'frontier' is the definition.
(I've seen this in another clue)
'road taken through south african' is the wordplay.
'road' becomes 'rd' (abbreviation).
'taken through' is an insertion indicator.
'south african' becomes 'boer' (Dutch settler in South Africa).
'rd' going inside 'boer' is 'BORDER'.
(Other definitions for border that I've seen before include "Frontier of a country" , "Perimeter - fringe" , "An edgy place" , "Edging" , "Frontier or edge as of garden" .)