But the idea is that when the sky falls the people will be locked up safely in their underground cages.

Bob Dylan always used to have a way of coming up with the fitting quote:

I will not go down under the ground
"Cause somebody tells me that death's comin' 'round
An' I will not carry myself down to die
When I go to my grave my head will be high,
Let me die in my footsteps
Before I go down under the ground.

This site has the rest of the words - and a RealAudio sound file of the man singing it too, except it didn't work for me. (The vandals took the handles, I imagine.)