Certain nothing will go through a rough course (8)
I believe the answer is:
truelove
'go through a rough course' is the definition.
I can't judge whether this defines the answer.
'certain nothing' is the wordplay.
'certain' becomes 'true' (I can't justify this - if you can you should believe this answer much more).
'nothing' becomes 'love' (love means zero in tennis).
'true'+'love'='TRUELOVE'
'will' acts as a link.
Can you help me to learn more?
(Other definitions for truelove that I've seen before include "Quatrefoil" , "'The course of ... ... ne'er ran smooth'" , "'The course of ..... ne'er runs smooth'" , "''The path of . . . . . . . . ne'er runs smooth''" , "dearest" .)