Vespers — last couple not staying still (4,2)
I believe the answer is:
even so
'still' is the definition.
(both can mean 'nonetheless')
'vespers last couple not staying' is the wordplay.
'last couple' means two replacements for 'last'.
'last' says to take the final letters.
'last' becomes 'even' (I can't justify this - if you can you should give a lot more credence to this answer).
'not' becomes 'o' (I've seen this in other clues).
'staying' indicates putting letters inside (stay could historically mean to imprison).
The last letter of 'vespers' is 's'.
'even'+'o'='eveno'
's' placed into 'eveno' is 'EVEN SO'.
(Other definitions for even so that I've seen before include "however" , "'Nevertheless (4,2)'" , "'Despite, still (4,2)'" , "'Nonetheless (4,2)'" , "Nevertheless, albeit" .)