Never underestimate your adversary

from here and here (image source)

I don't know, maybe if the gate was on the other side of the door the dog might not have been able to tear the door apart. Another possiblity might be one of those metal kick plates for the far side of the door, since the dog probably started tearing at the bottom and the metal should help prevent that. The key point, though, is to be aware of what kind of attack your defenses are likely to face, evaluate them on whether they are up to the task, and add additional layers to address weaknesses.