What do you mean by 'exposed'? Are we talking cracking of the resin and individual glass fibres sticking out into the water (which would be unsafe), or just being able to see the composite? The materials they're using (well, at least nemo and specialfins, I haven't dug under the rubber on the leaders) these days aren't exactly the fibrous mat and some glue that you pick up from the hardware store. They're high-end expensive woven fabrics embedded in resins specific to flexible underwater use. You can rub this stuff against your face all day without adverse effect. Unless some part of the fin actually breaks, then rubber edging should be fine to make them perfectly safe for hockey.

These types of fin are already dominant in the UW rugby scene, with most of the top teams wearing them near exclusively. As far as I know there have been no negative safety reports as yet.

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