Try adding this linetype definition:
*FENCELINE4,Fenceline square []-----[]----[]-----[]----[]
S,.0001,[BOX,ltypeshp.shx,x=-.1,s=.1],-.1,0.65,-.1,[BOX,ltypeshp.shx,x=-.1,s=.1],.0001
In a linetype definition A keeps distances exact and adds line segments on the ends.
S doesn't add line segments at the ends, it adjusts the lengths of the line segments in between.
Make sure PLINEGEN (System Variable) is set to the default value of zero(0) so the endpoints will be at each vertex of the polyline.
Undocumented since AutoCAD version 9 but still works.