Settle always has dog across it (3,2)
I believe the answer is:
pay up
'settle' is the definition.
(paying up is a kind of settling)
'always has dog across it' is the wordplay.
I cannot quite understand how this works, but
'always' could be 'ay' (archaic term for 'always') and 'ay' is found within the answer.
'dog' could be 'pup' (I have seen 'Young dog ' mean 'pup' so perhaps 'dog' could also mean 'pup') and 'pup' is present in the remaining letters.
No letters remain.
This explanation may well be incorrect...
(Other definitions for pay up that I've seen before include "Hand over the money" , "Discharge a debt" , "Settle" , "Give me the money!" .)