Kayak pedaling shoes?

Where clipins really help are during long distance pedalling when pulling back on pedals relieves the push on pedal muscle group. Tightness is adjustable and I keep my yak pedals much looser than bike pedals.

I haven't used clip-in pedals, but I'm sure they would reduce fatigue. In my case, when I get tired, my feet tend to slip off the pedals (that is, my feet slide down into the yakgina area), so I know I'm using some energy to hold my feet up in the air. I've thought about rigging up some kind of "heel clip" pedal system (as opposed to toe clip pedals) to help with that...