When I put my rods together, I press hard enough on the ferrules that the rod is hard to take apart again. Don’t overdo it, but make sure that the ferrules are seated properly. That makes sure that it won’t come apart during fishing and the the ferrules don’t slowly begin slipping. It’s when they slowly begin to slip bad things happen. A loose ferrule has a little bit of wiggle room and is not contacting properly over the entire length/surface of the joint and that causes a (quite) weak point.
Rod makes take great care to properly match the ferrules, but with use, wear, tear, time and age, all ferrules can (maybe even will?) begin to slip. Usually a good setting every now and then during the day is more than sufficient to keep the rod properly together. Waxing the male part also helps a great deal, but I’ve refrained from waxing for some years now. I find the wax attracts dust and even worse, sand. There are a few companies out there that makes a “dry wax”, but I’ve yet to try it out. It’s when the male part of the ferrule “bottoms out” in the female part (shut up, don’t say it) that it begins to develop wiggle room in the open end. Once I’ve successfully fixed this be *very* carefully sanding down the male part, twisting it into the female part for long enough to develop heat, feeling with my lips where the high spots were. By keeping at it, going *very* slowly I was able to get the ferrule to seat properly again. But - I’ve also been very unsuccessful in doing the very same thing.
I have several rods that are coming loose every now and then, all of them Hot Torpedos. No no, just kidding of course :-). I have one, a 20-year old 13’ 8-9wt, but it’s rod that’s dear to me, so I use it and do what I can to keep it going. And somehow the problem seems to be more outspoken and happening more often on DH-rods? Not sure this is really so, but it’s also often said that repeated spey casting over several days will twist rod part from each other. I’ve never had this happen to single handers. There is a lot more pressure on a DH-rod of course.
Anyway, taping the troubled ferrule on the rod completely eliminates the problem and I can fish it for a week without the ferrule coming loose. So I always keep some electrical tape (remember it needs to be water proof) in the salmon-gear-bag. Just remember to start the tape on the bottom ferrule and wrap it, so the twisting motion doesn’t just loosen the tape, but in fact tightens it. If you use wax, also remember to keep a handful of Q-tips in the bag. Just to be able to remove sand or dust that might have been trapped int eh female section.
Seat the ferrules properly every time, keep them clean and shop shape and you should be good to go for years.
Have a great weekend!
PoD: The trouble ferrule (you can see the wear) and the cool of electrical tape.