Accomplice to fence a red model (11)
I believe the answer is:
confederate
'accomplice' is the definition.
(confederate is a kind of accomplice)
'to fence a red model' is the wordplay.
'model' indicates anagramming the letters.
'to'+'fence'+'a'+'red'='tofenceared'
'tofenceared' is an anagram of 'CONFEDERATE'.
(Other definitions for confederate that I've seen before include "Ally" , "American soldier" , "Allied" , "Accomplice, fellow worker" , "Joined by agreement or treaty" .)