1. It takes 2 seconds to select the tank and cast protect on him, so unless he is very far away from you, you will get protect on him.
2. The secret to keeping a tank alive when he pulls a lot is to hit the heal button. When the heal button is off cooldown, hit it again! Congratulations, you now heal almost as well as a healer who is 100% skilled in his class. The only times the tank will die now is if the tank overpulls/doesn't know how to use defensive abilities at the right time, or you have really bad gear.

If the tank dies, it is his responsibility to advice his playstyle so that he doesn't die. You keep on pressing that heal button to the best of your ability.