Model and I see sharp part of a soldier's defence? (6,4)
I believe the answer is:
formic acid
'part of a soldier's defence?' is the definition.
(acid used by ants - soldier is a type of ant)
'model and i see sharp' is the wordplay.
'model' becomes 'form' (both can mean to mould or shape).
'and' is a charade indicator (letters next to each other).
'see' becomes 'C' (the word for the letter, according to Chambers).
'sharp' becomes 'acid' (as in sharp-tasting).
'form'+'i'+'c'+'acid'='FORMIC ACID'
(Other definitions for formic acid that I've seen before include "Substance emitted by some ants" , "Tannery chemical" .)