Shelters including free weapons (8)
I believe the answer is:
tridents
'weapons' is the definition.
(trident is a kind of weapon)
'shelters including free' is the wordplay.
'shelters' becomes 'tents' (tent is a kind of shelter).
'including' is an insertion indicator.
'free' becomes 'rid' ('rid' can be a synonym of 'free').
'tents' going around 'rid' is 'TRIDENTS'.
(Other definitions for tridents that I've seen before include "Forks for the sea-gods" , "missiles" , "Spears with three prongs" , "Weapons" .)