You can fish running leads that drop off so that would be my choice in the situation above if you were stuck on fishing running leads . Think they would work well in this situation you describe better than if casting into weedy area's where I wouldn't be convinced that the lead would eject, bringing the fish / lead into weed it should drop off on impact with the weed .
Also I've used running leads on some of the countries fastest rivers with no issues as you can't fish them slack obviously because of the current.