Several years ago, my boss insisted on doing this--putting a post at each end and corner of a fence. As the other responses indicate, there is no known mechanism for doing that automatically, short of writing some code, but that's not a linetype. I did a lot of research, but I wound up having to draw the fence and insert an array of post blocks... which meant redrawing the whole length of any segment that changed. Sorry. Hope you find a better solution.