With a spell on ship's security detail (9)
I believe the answer is:
watermark
'security detail' is the definition.
(a watermark may be used for security purposes)
'with a spell on ship's' is the wordplay.
'with' becomes 'w' (abbreviation).
'spell' becomes 'term' (I've seen this before).
'on ship' becomes 'ark' (as in Noah's ark. I am not sure about the 'on' bit.).
'w'+'a'+'term'+'ark'='WATERMARK'
(Other definitions for watermark that I've seen before include "Paper manufacturer's identification" , "Security device, on paper" , "Line showing maximum flood level" , "faint pattern" , "Design in paper" .)