Go straight over rocks, following troops (4,4,4)
I believe the answer is:
mend ones ways
'go straight' is the definition.
(both can mean to improve one's behaviour)
'over rocks following troops' is the wordplay.
I cannot really understand how this works, but
'over' could be 'on' (physically on top of) and 'on' is located in the answer.
'rocks' could be 'sways' (I've seen this in another clue) and 'sways' is found within the answer.
'troops' could be 'men' (I've seen this in another clue) and 'men' is found in the answer.
This explanation may well be incorrect...
(Another definition for mend ones ways that I've seen is " reform".)