(Marston may have presented it like there was nothing supernatural about it, but if you can lose it just because a man puts his foot on a lump of sand, it's magical).

Or legal!

Golden Age Athena held a patent on Amazonian training, and licensed it to Aphrodite under stringent terms. No men on Paradise Island is part of the terms. If they let a man step foot on the island, their license is revoked!