I work in a hospital that is going on 50 years old, and a lot of the water shutoffs are hard to find or they cannot be shut off completely. So for the past year, if I can’t shut off a water line to fix it or to replace a fitting, I freeze it.
I use a pipe-freezing kit called Cold Shot. You take the special fittings to clamp around whatever size pipe you are working on and freeze it. It takes about 3 to 5 minutes, and then you have about 10 minutes to work on it. I have to say, it has paid for itself in the last year.