Wow...those Canon white lens hoods must be made out of woven carbon fiber imported from volcanic carbon deposits at Reunion Island and bonded with a special resin from a rare African tree that grows only in a narrow band of the Ethiopian highlands.
At least that helps explain why the woman two weekends ago was extremely upset and very hard to talk down.
I was shooting in the wetlands, and a woman who stopped to talk about a bird we were looking at had a Canon something-or-other DSLR with a nice white (big) 400mm lens. We both held out our lenses over the water from a boardwalk pathway over the swamp (my Tamron 200-500 has a huge lens hood too), at about a 35 degree downangle. I zoomed in and focused, and she zoomed in and made a swish-plop! noise. She let out a gasping yelp like someone stepped on her foot, and I noticed her lens looked a whole lot shorter. Not only that, but neat concentric ripples were arching out from beneath her...while the bird I wanted to shoot was now flying away in fear. I guess the hood wasn't locked down right...and it just went right off the end of her lens and into the nice black alligator-ridden swamp.
I tried to console her with the usual 'at least it was just a hood'...not realizing the sucker costs $500-600! She wasn't getting any more relieved either...so I take it she knew what they cost. She wasn't even from around town, and asked where any used camera stores might be - I told her of the only one I knew in the area, about 10 miles away. She marched off - her photo day over - as in the bright Florida sun she didn't have much hope of shooting without it.
I'm thinking of making some kind of tether system for the lens hood, as insurance...even just something like a string that can neck around the lens and attach to a velcro tab or something. Though fortunately my Tamron's huge lens hood appears to be made out of plain-old plastic, and my lens itself only cost 1 3/4 Canon lens hoods!