Fight to guard one’s territory? (5)
I believe the answer is:
fence
This might be a double definition.
'fight' is the first definition.
(fencing is a kind of fighting)
'guard one's territory?' is the second definition.
'fence' can be an answer for 'guard' (thesaurus). I'm not certain of the 'one's territory?' bit.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for fence that I've seen before include "Barrier; deal in stolen goods" , "Bound over this" , "Fight with sword - barrier" , "Handler of stolen goods" , "Stolen goods dealer" .)