Is there a way to turn the flash totally off in the HDR-HC9, using it a Gate Underwater housing and sometime the flash goes off, when I doing a still photo and wrecks the photo since it bounces inside the hosuing.

Should be either a small switch on the side labelled with a lightning bolt looking icon - you'll see flash modes switch on the display as you cycle through, look for the "no flash" (bolt in a crossed circle). Not sure if this setting holds when the camera is power cycled though - you might dig into the menus and see if there is a flash off option.

OR, mount any filter or lens on the front threads, there's a switch there in the threads that shuts off the flash.

Sorry I can't be more specific, been a while since I owned the HC9, but those are typical Sony features, one or more should work for you!

I have the HC7 in a Gates housing, so basically same setup is you, and I've been using it for about 17 months. As Dave says, pressing the flash button until the lightning bolt with the slash will turn it off. The setting holds for awhile, including cycling the camera power on and off, but I have noticed that the setting can "wear off" after some time. So, besides trying to be dligent about making sure the flash is off before getting in the water, I've also covered covered the depressed flash with some electrical tape - to ensure that the flash won't go off.

As far as having something in the threads on the front of the camera - I don't find this to be true with the HC7. I shoot with a +10 diopter attached most of the time and still find that the flash will try to open and fire if the above steps aren't taken. Maybe that's a menu item somewhere?