Way to enter South African frontier (6)
I believe the answer is:
border
'frontier' is the definition.
(I've seen this in another clue)
'way to enter south african' is the wordplay.
'way' becomes 'rd' (short for road).
'to enter' is an insertion indicator.
'south african' becomes 'boer' (Dutch settler in South Africa).
'rd' inserted inside 'boer' is 'BORDER'.
(Other definitions for border that I've seen before include "Bound" , "Line between countries" , "Type of sheepdog" , "Rim" , "Frontier or edge as of garden" .)