That fully sux.
I've ripped my feet on reef a couple of times and tried everything from "spray on skin", elastoplast, bandages, betadine, savalon, yadda yadda .. none worked.
My open wound was getting worse because the water makes it soggy, and it just doesn't heal so well..
Someone introduced me Lucas Paw-Paw (in a red tube/tub from chemist & others).
It's an oily goo, which means water resistent, so bung it on, wrap in your favourite strapping, and you're good to go. It 100% keeps water out of the wound, and also helps it heal without a scar.
Yes, I am a raving fan.
Doesn't instantly fix your foot, but it's a big help.

Best of luck on a fast heal (heel?)

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lucaspapaw.com.au/