Mariner heard behind another person making descent (8)
I believe the answer is:
abseiler
'person making descent' is the definition.
(someone abseiling down a building)
'mariner heard behind another' is the wordplay.
I cannot quite understand how this works, but
'mariner' could be 'ab' (short for able seaman) and 'ab' is located in the answer.
'heard' could be 'e' (I've seen this in other clues) and 'e' is found in the answer.
'another' could be 'r' (I've seen this in other clues) and 'r' is located in the answer.
The remaining letters 'sile' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for abseiler that I've seen before include "One descending using ropes" , "taking rope down" , "one clinging to cliff-face?" , "One descending on rope" , "who has an on-line comedown" .)