Many require the protection of fencing (4)
I believe the answer is:
mask
'protection of fencing' is the definition.
'mask' can be an answer for 'protection' (mask is a kind of protection). I'm not certain of the 'of fencing' bit.
'many require' is the wordplay.
'many' becomes 'm' (Roman numeral for a thousand).
'require' becomes 'ask' (synonyms).
'm'+'ask'='MASK'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for mask that I've seen before include "Face-cover" , "cloak" , "Cover for the face" , "Screen" , "Camouflage" .)