Old sailor damages hot saline boggy area (4,5)
I believe the answer is:
salt marsh
'saline boggy area' is the definition.
(a salt marsh is a salty, boggy area)
'old sailor damages hot' is the wordplay.
'old sailor' becomes 'salt' (old-fashioned nickname for a sailor).
'damages' becomes 'mars' (marring is a kind of damaging).
'hot' becomes 'h' (abbreviation eg on taps).
'salt'+'mars'+'h'='SALT MARSH'
(Other definitions for salt marsh that I've seen before include "Boggy ground" , "grazing area" , "regularly flooded area" , "squishy territory?" , "Land sodden with sea water" .)