Sometime somewhere I saw a tool that would allow me to reach under a
bathroom sink and turn off a very hard to turn cutoff valve. Believe it
or not, I cannot get to the valve to turn it off unless I totally
disassemble the plumbing, which I hope not to do. Does anyone know where
to find that sort of tool? I don't even remember what it looked like,
but it seem to have an oval pocket to engage the oval knob on the
shutoff valve.

I'm sorry this explanation is not better.