Soldier next to favourite railing (7)
I believe the answer is:
parapet
'railing' is the definition.
(I've seen this before)
'soldier next to favourite' is the wordplay.
'soldier' becomes 'para' (short for paratrouper).
'next to' is a charade indicator (letters next to each other).
'favourite' becomes 'pet' (synonyms).
'para'+'pet'='PARAPET'
(Other definitions for parapet that I've seen before include "Wall at roof's edge" , "place of safety?" , "Militarily, it protects" , "wall used for protection" , "Low wall along the edge of a balcony" .)