HP Questions Upon Re-reading: Book 1 Chapter 7(2)
I also wondered why Professor Dumbledore specially mentioned about the room hosting Fluffy the three-headed dog in the school opening feast? With his skills and power, surely, he can cast a powerful protection spell over the entrance and stop any underage students from getting past. Of course, all that effort could just be him setting a training adventure game for Harry. If he truly wished for a foolproof security system, what could be better than him carrying it all the time? As the most powerful wizard of the century who is alive, we can safely assume none would dare to attack or steal things on him personally.