While the dogs are in ready-to-pounce position, they are invincible

[ShnitzelKiller]

When they notice you, they hunch their shoulders and growl before attacking, and in this phase, even throwing a propaine tank right next to them and exploding doesn't affect them at all. Which really makes it a hole lot harder to time it right so that it doesn't explode while you're holding it or when they have just noticed you.