Marches dull guards arrange (10)
I believe the answer is:
borderland
'marches' is the definition.
(I've seen this before)
'dull guards arrange' is the wordplay.
'dull' becomes 'bland' (similar in meaning).
'guards' is an insertion indicator (inserted letters are guarded).
'arrange' becomes 'order' (ordering is a kind of arranging).
'bland' enclosing 'order' is 'BORDERLAND'.
(Other definitions for borderland that I've seen before include "region close to frontier" , "marches" .)