When I first got the clipless I road around in the yard so that I could do all my early falling on the grass (much more forgiving).

I unclip my foot whenever I am approaching an intersection so I am ready to stop if I need to, I've never had a problem with the foot accidentally clicking back in, but then, since I'm anticipating the possible need to stop, I'm not really putting much effort on the pedals. If I know I really need to stop, I generally extend my leg down and slightly out, ready to hop off, plus, in my own mind, I think it gives drivers an added visual clue that I am about to stop, seeing as I have a foot that is nowhere near its pedal.