The following short “Oh Shit Award” comes from Filip (response below):
A long time ago I tried the following technique and I almost died: for rappelling on a single peg you needed to add a prusik loop (I think he means creating a rap cord loop into which to feed the rope - Ed), to the peg (nowadays quick-links or rappel rings are used). So after you rappel, the prusik was left behind. The technique I wanted to try was a special hitch that would loosen if you recuperate your rope, so you wouldn't lose your prusik. I had only tested it a few times in my garage. Of course, I should have tested this system with a backup rope. But I didn't - I was young and "invincible" or rather stupid.
So after climbing 50m on a crag, I thought: "why not try to use the technique here on the last bolt before the anchor?"
So I did and when I took away my lanyard and started to load my rappel rope I noticed the prusik was already loosening. I was standing in a corner with 50m emptiness between my legs. Luckily I still had 1 hand on the rock and could connect my lanyard again.
Never tried it again! I'll take enough prusik with me to leave behind if necessary. I realized my life is more important than saving a few bucks.
An important lesson is to not try special techniques unless you have practised really enough, and with a backup rope!
I'm guessing what Filip was doing was attempting a dangerous technique designed as a "leave no trace" method, involving a slip knot and a loop of cord or sling (the slip knot jams against the sling when you rappel on one strand of rope, but releases when you pull the other strand, pulling down the sling with it). Unfortunately such a technique also stands a good chance of leaving behind both a smashed body instead ("take only photos, leave only footprints, and no corpses!"). But his story highlights a few very important points:
Don't practice extremely dangerous techniques that have zero room for error in a position where any error would be injurious or fatal. This is why a BASE jumper generally does over a 100 parachute jumps from an aircraft perfecting their skills, “greasing the groove”, developing muscle memory, replacing “I think” with “I know”, and “I know” with “I no longer even think about it” (as in, where is my reserve handle?).
Be aware that knowing a little bit more than nothing can often be far more dangerous than knowing nothing at all. This is a common climbing forum issue, where someone throws out some badly thought out trick technique – something they once spent ten minutes practicing in their garage cellar – as if it’s THE method, something they use every single day. Seeing as forums are often like gladiatorial combat, alphas and omegas, such a person can come across as an authority to a novice, who may take what is itself barely understood by the author, as well as incorrect or missing key points, and try it themselves, not in a garage, but on a cliff face. I remember once seeing two climbers about to do a retrievable ice axe rappel of the top of an ice cliff (when there where rap points close by, and easy threads to make), one ‘experienced’ climber showing the inexperienced how it’s done (showing off). The ‘experienced’ one set it up, and was about to go over the edge, when I just walk passed and said “Let me have a look at your anchor”, and just pulled it out with a light tug (it was in a pile of snow they’d made, not in the ground). Instead of saying “thanks dude, you just saved my life”, the leader just looked cross because I’d made him look like an idiot (he was). Such people as this eventually come a cropper, and get impaled on their egos, but it’s not good to allow them to take other – less experienced – climbers with them.
Many dangerous techniques, like escaping from a submarine by swimming out of a torpedo tube, are developed as high-risk options when there you're out of options, and it’s worth knowing such ‘special methods’, and practice then, but keep then behind glass and only break in an emergency. The single rope rappel using a fifi hook and bungee cord is such a technique, one that could save your life sometime, but equally kill you instead. The releasable Bowling may look dangerous, but I’d not class it as an emergency technique, but rather the same as any other, in that you need to practice and understand it (if you do neither then yes, it’s dangerous, but so is tying in with a bowline).
If you’re trying out obscure techniques, like rappelling on karabiner break, think about doing it on a top rope first, so that you can make small mistakes without big consequences. Take a day down the wall or at the crag (wet days are ideal) and go through all the stuff you think you ‘know’, but have never actually done (i.e. you don’t know anything). This would include even basic stuff like Prusiking up a rope.
My advice on dangerous techniques is to treat them like you would learning to deadlift double your bodyweight, or shooting an apple of your child’s head: practice, practice, practice. Build up to the actual act or performance or demonstration of skill through repetition and practice in which failure will not result in a broken back or a bullet in someone’s head. Take that knot you saw on mountainproject.com and tie it a hundred times until you can do it easily, then nine hundred more. Play with it, test it, see what it can do, and what it can’t. Try and defeat it (and your ego), and see why it’s not written up in the SPA handbook.
Master it, own it, but don’t use it to demonstrate how smart you are, or how skilled, or better than other climbers. Instead, understand the work it took to grasp just how useful this technique could be, but perhaps only once in a lifetime of climbing, then place it behind the glass and hope you never need it.