How did the curse on the DADA job work?

Question

The facts:

• The job was cursed.

  Did Voldemort actually curse the job of Defense Against Dark Arts professor after being denied the position?

  Oh, he definitely wanted the Defence Against the Dark Arts job. The Aftermath of our little meeting proved that. You see, we have not been able to keep a Defence Against the Dark Arts professor for more than a year since I refused the post to Lord Voldemort. - Albus Dumbledore, Harry Potter and the Half-Blood Prince

• It lasted From 1957 until the fall of Voldemort (1998)

  In what year did Voldemort curse the DADA job

  1957 (Y-23) [Voldemort] resurfaces and applies to teach [Defence Against the Dark Arts] Ten years after the death of [Hepzibah Smith], [Voldemort] returns to [Hogwarts], where Dumbledore] refuses to grant him a teaching job. He then curses the [Defence Against the Dark Arts] position, and since that day, no professor has stayed for more than one year in that post. Again we don't know exactly when this happened, but since most evidence points to [Dumbledore] becoming headmaster in 1956 [[Y-24]], [Voldemort] couldn't have come looking for a job much sooner than this. (HBP20)

• No one could hold that position for more than one year

  Was Quirrell the Defense against the Dark Arts teacher for more than one year?

  It's well seen throughout the series that there is a "curse" on the DADA teacher position, that no one can hold that post for more than a year

Is there (preferably canon) information on:

• How did Voldemort manage to do such a powerful curse?
• Why didn't Dumbledore, knowing about the curse, not do anything to lift it?
• Why didn't Voldemort put that curse in the headmaster's position, or on the whole Gryffindor house?

Answer 1

I can try to answer only the last two, because there are no details in the book about how Voldemort cursed the job. We don't even know when he did it - right after meeting with Dumbledore or later. My only guess is, he was the best at the Dark Arts. Curses are Dark Arts. He didn't hesitate to use Unforgivable Curses. The DADA curse was maybe just a laugh for him.

Why didn't Dumbledore, knowing about the curse, not do anything to lift it?

Remember the curse in the ring that caused Dumbledore's hand to go lifeless? He couldn't do anything about it. Snape just held it for a little amount of time. Strong curses cannot be lifted. Think about the curtain in the mansion of Harry's godfather, the necklace... the list goes on. This kind of curse is not a tongue-hanging curse. I also suspect Dumbledore didn't even try. He has his style of doing things, sometimes letting things go.

Why didn't Voldemort put that curse in the headmaster position, or on the whole Gryffindor house?

The curse was like an action in a cold war. If Voldemort wanted to do bad things to the headmaster, he didn't need curses. Remember, at that time, Voldemort was gathering Death Eaters. He was preparing. The last thing he needed was a powerful enemy sacked from his most favorite position (he preferred this post to that of Minister for Magic, so figure out how valuable it was to him). A sacked Dumbledore is dangerous. When he is inside school, he is eccentric, peaceful and busy in doing normal things. In other moments, he is dangerous (Battle of the Century, building the Order of the Phoenix). I bet Voldemort was fearing that, the moment he cursed him, Dumbledore would be a bounty hunter for him. So, he did something that sure irritated Dumbledore, but not sinister enough to make him go after Voldemort. The same logic goes for cursing the whole Gryffindor house.

Answer 2

Regarding your third question:

Why didn't Voldemort put that curse in the headmaster's position, or on the whole Gryffindor house?

I think it's fairly obvious: he wanted that particular job, so he made sure that that position was empty and that Dumbledore had to look for a new Professor every year. He probably thought that at some point Dumbledore will either

1. run out of better candidates than him or
2. be bullied/harassed enough by the curse to give him the job

As for the first two questions, I have nothing to add to @cowboysaif.

Answer 3

As I argued in this answer, there probably was no curse, nor would such a curse have been possible. So to answer your three bulleted questions:

• How did Voldemort manage to do such a powerful curse?

  He didn't.

• Why didn't Dumbledore, knowing about the curse, not do anything to lift it?

  A non-existent curse cannot be lifted.

• Why didn't Voldemort put that curse in the headmaster's position, or on the whole Gryffindor house?

  There was no such curse.