I think self teaching either method is going to come with risks. That being said, I taught myself how to pop using videos online. It seemed like the safer method to teach myself. As long as you are careful (i.e. don't bend their spine) I think it's fairly easy to teach yourself how to pop. Also younger snakes are much easier to learn to pop with.
As far as I know I didn't damage any of my snakes while learning and I can do it reliably now.
It takes a while to learn, but palpating is also another method you can use. I wouldn't say it's 100%, but with larger snakes it will give you a pretty good idea.
http://www.moonlightboas.com/care-in...of-a-snake.php