A wood preservative Rose applied in shelter (8)
I believe the answer is:
creosote
'a wood preservative' is the definition.
(I've seen this before)
'rose applied in shelter' is the wordplay.
'applied' indicates an anagram.
'in' is an insertion indicator.
'shelter' becomes 'cote' (cote is a kind of shelter**).
'rose' is an anagram of 'reos'.
'reos' inserted into 'cote' is 'CREOSOTE'.
(Other definitions for creosote that I've seen before include "Oily liquid for preserving timber" , "Oily, smelly wood preservative" , "'Dark oily liquid, preserves wood (8)'" , "Wood preservative oil" , "Dark oily liquid, preservative for wood" .)