Protect hard border (5)
I believe the answer is:
hedge
I believe this is a double definition.
'protect' is the first definition.
(I've seen this before)
'hard border' is the second definition.
(Other definitions for hedge that I've seen before include "appear non-committal in statement" , "Protect oneself from loss" , "Fence formed by bushes" , "Shrub boundary fence" , "Windbreak" .)