Caliper

I've mostly ridden road bikes since childhood and 99% of the time with clipless pedals. Currently I'm trying to improve my MTB skills and am caught in between clipless and flat pedals. So far I have mostly used clipless because I am more comfortable with them but want to get better at flats. On the one hand, flats allow me a quicker exit in technical situations, but on the other hand my feet lose the pedals on small drops and bumpy descents, which really scares me due to the speeds involved (as long as the descent is fairly straight, haha). I hear people say that this doesn't happen "with the proper technique", but am having a hard time finding tips on what these techniques are. Does anyone have some pointers or youtube links for this? I'll be upgrading my flats soon to something like a Chester and currently have the options of tennis shoes, lightweight hiking boots or MTB clipless shoes to ride in but still don't know what to do with my feet except push down on the pedals?