Having never done this, this is my theoretical approach.
Get a brass grommet kit from Home Depot and install a grommet in the middle of the achilles heel of each foot pocket. Pre-score your hole then lightly heat up your hole-punch to get it through the thick rubber w/o tearing.
If you want to be real fancy you can find SS grommets to use instead of the brass.
Now before you do all this, you might want to envision your securing strap first.
Get a brass grommet kit from Home Depot and install a grommet in the middle of the achilles heel of each foot pocket. Pre-score your hole then lightly heat up your hole-punch to get it through the thick rubber w/o tearing.
If you want to be real fancy you can find SS grommets to use instead of the brass.
Now before you do all this, you might want to envision your securing strap first.