Mine have been battered against loads of rocks, stood on them with the blade folded under on rocks and chucked onto the rocks when getting changed and they're fine, allbeit a very scratched.
OMD's broke right near the footpocket if I recall correctly, if not right between the two screwholes so nothing to do with hitting rocks I'd guess.
They're far from fragile so don't be scared mate, you may bang you head while finning along looking back at your finless legs the first time you use them though
