It is best to use 1 3/4 inch 9 gauge galvanized staples, to attach the wire to the posts.  This is because "they have 50% more resistance to pull out than 1 1/2 inch long staples" (Savage, 1989).  The slash cut pointed staples act as a wedge and force the legs to curve away.  This will maximize holding power.  It is not recommended to use staples that are single legged, or have diamond-shaped points.