the term for one or more border rows of polys that help control smoothing is coplanar polygons -- the trick is, as the name implies, that the coplanar polys must lie in the same plane as the face whose shading you're trying to control. in anthony's illustration the coplanar polys can be seen on both sides of the edge connecting the shaft to the top of the backpack. for a sharper edge, use narrower coplanars and use wider ones for a softer edge.