Its been SOP for several years to mark BOTH ends of the portage.  (I also use a small customized waypoint symbol to mark those ends.) This serves a number of purposes, not the least is being able to retrace your steps in the event you have to back out of part of your route (e.g., blocked by forest fire).  But there is another reason for doing it.  I've run into a few instances where the portage was marked (on one end) at the wrong location.  If one end is correct, and the length of the portage is not too long, you can make a stab at estimating where the portage might be based on the topography between the two bodies of water if you know where you are supposed to end up.

Hmm.  Flat tire!  I had one of those as I pulled into the Onnie parking lot last year (my shuttle driver taking me on to Leano was gracious enough to help me change it).  After my trip, I had it repaired in Red Lake before setting out on my trip home.  Mine was caused by what looked like a long screw for drywall (or maybe a screw used on some decking material).

dd