its a flick. not a kick. thats key. its all one quick snap of the ankle. also, try leaving more of your foot on then you would expect. i have most of my foot on, but at an angle. by doing so, the board will come up and meet your feet, rather than the hideous flick-it-and-pray-you-land-on-it style kickflips. and if it IS coming up to your feet so you catch it, you should actually catch back foot first, thus making that problem easier.
id also guess if your back foot is coming off its because you arent staying over it enough, you are leaning too far over your back foot. hope that helps