I learnt them over 20 years ago and that’s never happened to me. I know what you mean though, I’m also scared of super waxed ledges and I kinda get that paranoia when I want to try backlips on ledges.
Get comfortable with locking into them on unwaxed curbs first then start trying them on obstacles where you know this won’t happen. Backtails feel so good, you want them in your life!
Thinking about it, it’s quite odd but, a trick that essentially puts you into a back tail that I could do was switch back heel to front nose.
Never slid out on those but you do end up in the same position as back tail.
Maybe it feels more controlled than ollieing into that position.
You know what’s really weird (for me at least)? Doing them on ledges on top of banks is really different from doing them on ledges. I imagine it’s the same on miniramps. The way you have to move your hips and shoulders to lock in properly isn’t the same at all. I have to learn them on ramps now.
Clip from last summer in London while we’re at it:
Back tails are one of may favourite tricks ever, I never could do them on decent sized ledges and they are never long or good looking but regardless, they are one of the best feeling tricks.
I learnt kickflip backtail slides in the mid ninetees though and without the flip way later which I guess is weird.