Thanks for the love, y'all.
With the back foot thing, it's more of a set-up thing so that I land with my back foot more centered (both laterally and vertically) and the sole of my shoe isn't touching the ledge. It also feels like it pushes my baseplate against the ledge and locks it better, as well as being able to stand on top of it easier. I wish I could explain with a picture, but imagine you're board as an x(width) and y(length) axis. I'm mainly talking about moving your back foot further up the y axis instead of being right on the edge of the tail. Less on the edge and more ON it. Might have been a personal problem that not everyone has, since i've been making that adjustment on a lot of tricks lately.
As for the slipping out, I had the same problem and it actually messed with my wrist pretty bad, which made me stop really going for them for a while. I don't think I would've realized it at the time, but I wasn't fully committed and standing up on top of it, which was making me slip out. Once I was really on top of it and had my head and shoulders looking OUT of the slide ready to come out to regs, I stopped slipping out and actually stuck a few times, which was weirdly refreshing, after slipping out constantly, cause that just meant I had to go faster and push on my back toes a bit more.
Whew, just typed an essay, but anything to get those sweet sweet back tails.