I've heard of setups where a guillotine has been constructed with a bar across the bottom behind where the neck would go so that when the moment is right, i assume when one or both of you are cumming, your partner can pull the lever and you get a nice satisfying thud as the blade hits the bottom.
Danger in general is sexy time spice, my gf is VERY into hard choking. We've had to tone it down a bit as we've become more experienced with it though