I don't know how others have fixed this, but here's how I've fixed it. Any of several ways:
1) put a single wind (or two depending on how wiggly/loose it is) of black tape around the male portion. It only takes a single wind most of the time, because otherwise you won't even be able to get the rod to start being inserted
2) Add a dimple or dot of JB weld (or any other such contact cement type of hardener plastic compound) on to the inner tongue part that pushes up and down with the clasp. Let dry, then sample the snuggness. Start very small at first, because, if you find out it's still not creating a snug enough contact, you can always increase the thickness with a second go-round. Likewise if you made it too thick (clasp won't even shut), you can always file or grind back off a bit, to decrease thickness of that dimple/spot.
3) For field emergencies (rod keeps sliding down) I have sometimes had to scrounge for a toothpick type twig or splinter of wood, to use as a shim, shoved into the wiggle crevice

Or, since I always carry a roll of black tape in the zipper portion of my apron, I've found myself doing a quick few winds to booger up the outside of the two rods connection point. Of course that means you'll no longer have an adjustable rod for the time-being, but it works for a quickee in the field.