Persist in spite of difficulties (7,2)
I believe the answer is:
soldier on
'persist in spite of difficulties' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for soldier on that I've seen before include "Persevere (colloq.)" , "Doggedly continue" , "... to bear up" , "Keep struggling" , "Don't give up" .)