Speedplay Zeros have no float... they are made for racers who need to be locked in that way. My son used them when racing and he couldn't get out of them a few times. Ten years later, they are sitting in my basement.
I have been using Speedplay X pedals for about 8 years; they are perfect. They are not advertised, as they were the precursors to the Light Actions, but you can't accidentally clip out as easily. They are still sold, though. I would recommend them to anyone. I switched from SPDs and that solved the knee pain I was having.
I have the Frogs on my other road bike. I don't like them as much, as I had a learning curve of not unclipping by accident. But, I needed/wanted mountain pedals on this bike and I know I can't ride 50-75 miles on spds without agony.