For the last fifteen years about half of all my riding has been commuting, and much of that on folding bikes, so no foot retention. The other half of my riding, and more in the last couple years, is on bikes with SPD pedals. I still have clips and straps on a couple bikes but rarely tighten the straps so that's pretty much like platform pedals anyway.

Either way, with SPD's or without them, if I think about it I aim for about 100 rpm, which I check by humming "the hustle" or Mozart's Turkish March as I pedal, while practicing a smooth pedal stroke and all that. Honestly I don't think about pedaling very much. Most of the time I pay no attention to my cadence or stroke, but even so I doubt my cadence falls much below 90 rpm.

Towards the end of a long ride on the fixie, getting up any kind of a long steep hill becomes a real challenge, and of course my 100rpm cadence is long forgotten by that point. That's when I start pulling up on the pedals. Pulling up involves muscles that until that point I probably haven't used, so those muscles may be pretty fresh even late on a ride.

I don't recommend it to anyone, but that's pretty much what I do.