Why was Dumbledore afraid that Voldemort will get the prophecy? Looking at the prophecy I can't see anything that would help Voldemort and give him new information that would be dangerous for the Order.
"The one with the power to vanquish the Dark Lord approaches... born to those who have thrice defied him, born as the seventh month dies... and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not... and either must die at the hand of the other for neither can live while the other survives... the one with the power to vanquish the Dark Lord will be born as the seventh month dies...."
Voldemort only knew about the first part. I can't see anything in the second part that would have valuable information.
So: Either there is some meaning in it that I didn't understand, or the rest of the prophecy really was useless, and I can't see why Dumbledore would put the Order in danger just to guard the prophecy.
Dumbledore might have wanted to trick Voldemort into thinking the prophecy is important and make him waste his time by directing his efforts to the useless prophecy. If you can give me evidence for that it would be great.