I agree with you denverd0n. "if you are deliberately knocking broken glass into the water, you are being very irresponsible."
After watching quite a few videos on sabering now, I am even more convinced that this is just really stupid. A great way to end up with a shard of glass in your hands or face.
Here are a couple of sabering videos that people should watch before trying this. Might change their mind or at least persuade them to put eye protection on.
https://www.youtube.com/watch?v=Osa_kK7msSYhttps://www.youtube.com/watch?v=CcvUcQIMpog