People need to stop thinking stacking balances a card like this. You aren't going to get 6 of them out by the time you need them.
It's a great card, but it simply needs to be stronger.
For starters, it has to be cheaper if it's going to protect a combo, because the combo has to drop fast. And again, 1 is just too little.
Try:
3 life
Stops 3 damage
Upgraded,
2 life
Stops 3 damage.
That way it will actually keep that rustler working (except for freeze, lobo, reverse time, permanent control, shockwave, rage potion, lightning bolt, and mutation)