What is done to protect national treasures such as the declaration of independence?

They're kept in the city most likely to be nuked in the event of a real war.

What the other answerer's said are true about the security.But sometimes I highly doubt that the government would allow such an important document to be displayed like that.I mean that is the basis of our entire country so what if the city was nuked or something horrible like that,even though that is highly unlikely,the document would be destroyed before someone could sound the alarm.

There is serious security. If you go to Washington, D.C., you can see these documents. They are encased in glass and have guards around them. They have sensors to make sure nobody touches them or removes them, and you aren't allowed to take flash photographs of them, because you might fade them. At the end of the night, or in case of emergency, the documents are lowered into a vault below the building that is resistant to the elements. No worries that any harm will come to these documents!

well that piece is in washington and is behind like 2" of bullet proof glass, has special sensors all around it, I believe 4 guards at all times in the room, armed.....and if a sensor goes off, it flips away and travels 4 stories underground to a locked box.

special items that we hold as a government are protected better than fort knox.

If you ever watch the movie national treasure you could get a pretty good idea how it is protected assuming the information is factual.