Try adding a coat of Shieldz Clear, it's used to prep foil wallpaper for paint. It will help the epoxy stick to the foil--but it won't make it stick forever. But, as with any paint/coating, you're only as good as your weakest link... adding coats of epoxy will not make any difference once a deep enough scratch is made in the epoxy because it just won't stick to the slick surface of the foil.
-Dave
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