border vs fence line

border and fence line both are nouns.

Word	Noun	Adjective	Verb	Adverb
border	Yes	No	Yes	No
fence line	Yes	No	No	No

As nouns, fence line is a hyponym of border; that is, fence line is a word with a more specific, narrower meaning than border:

Other hyponyms of border include circuit, circumference, property line, state boundary, state line.

border (noun)	fence line (noun)
a strip forming the outer edge of something	a boundary line created by a fence
a decorative recessed or relieved surface on an edge
a line that indicates a boundary
the boundary of a surface
the boundary line or the area immediately inside the boundary

border (verb)	fence line (verb)
lie adjacent to another or share a boundary
extend on all sides of simultaneously; encircle
enclose in or as if in a frame
provide with a border or edge
form the boundary of; be contiguous to