Contending successfully with a course of masonry (6)
I believe the answer is:
coping
This clue could be a double definition.
'contending successfully' is the first definition.
(I've seen this before)
'course of masonry' is the second definition.
'coping' can be an answer for 'course' (I've seen this before). I am not certain of the 'of masonry' bit.
'with a' is the link.
Can you help me to learn more?
(Other definitions for coping that I've seen before include "Rubbing along" , "wall feature" , "Doing well" , "Contending with - wall masonry" , "Sloping top of a stone wall" .)