
Please note a few things about this story:
1. The movies have always shown Hogwarts up on a cliff. I have always imagined Hogwarts down low on sprawling lawns leading down to the lake and off into the woods. There are many many castles in the UK and surrounding countries that are right down on the water.
2. Just because you haven't read about the characters trying something yet doesn't mean they haven't tried it.
3. If they just magicked themselves out of every situation there would be no story.
4. If you find yourself saying, 'that's dumb, why didn't they try this, that, and the other', pause for a moment and consider that they tried it and it wasn't written about, or that you haven't gotten that far into the story yet to see them do it.
5. Why it all happened is a mystery to the characters, so it takes a while to be revealed in the story.
Just a few considerations after reading over some of the reviews people have left. Often people comment the characters (or the writer) is stupid for not doing things, but they haven't read far enough into the story to see them do those things.
P.S. This is his 5th year but Umbridge isn't in this story.