Can I run with an Apple Watch in the rain?
There's no way to turn the touch input off temporarily, but you can prevent the Apple Watch from stopping workouts early. When you start a workout just go to the watch face the way you normally would, the Workout will run in the background and can't be stopped until you go back to the app and it stop it yourself. It's not perfect, as you can't see your live progress, but it still works.