I would say - simply practice so you don't do that!
Practice on fruit - so you can cut the fruit & check your depth
Practice on reel skin
Practice & practice & practice till you know your machine inside out & upside down/ you know your handspeeds/ your needle depth - all which only comes from experience & practice.
heads up I have blowouts on tattoos done by experienced tattoists - it can happen to the best folk - but I would not want to replicate that and it is something I would do all I can to avoid if possible -.
I would rather (if at any point in the future) I am tattooing that a client comes back for a touch up - than cause a blow out - I know it will happen ! and a wee piece I did on my husband - someone thought it might have a wee blow out on it - I am inexperienced and still a total newbie and just trying to learn and make sure anything I do to the best of my abilities
Because blow outs seem to be the worst mistake one can make when tattooing people.
So I was hoping somebody knew of a practice medium, eg a particular kind of fruit, that will blow out when tattooing too deep.
they tattoo pigs for identification, ask if you can do some of those,
however, as said previous by Kiaran, prectice until you drop.... everyone will at some pointy have a blowout, there are too many factors to be ble to prevent it 100%, your aim is to be at a level of skill and comfort where you can make it as avoidable as you can. If you go out of your way to create them, it will be harder to avoid them in future, trust me.