If you are off to Indo or tackling something that might slap you, step up to a 7.4mm leash. The increase in diameter from 7.0mm gives you 10% more cross-sectional area, thus more strength in the PU cord.
If you want to be xtra sure, go for an exra foot on your regular length. You'll get extra stretch and release on that critical go-down in front of the reef.
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