Drive back concerning sign of life (7)
I believe the answer is:
repulse
'drive back' is the definition.
(synonyms)
'concerning sign of life' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'sign of life' becomes 'pulse' (a person's pulse).
're'+'pulse'='REPULSE'
(Other definitions for repulse that I've seen before include "Beat off -- rebuff" , "Drive back or reject" , "Fend off" , "Check" , "Ward off" .)