Preventing a Mask From Animating

This should be pretty simple, but I'm having no luck.

I selected a layer with some text on and then created a mask over it making the text invisible.

Then when I want to animate the text and move it from behind the mask so it's now visible the mask moves with it. Is there any way to keep the mask in it's place and not move with the text.

I also tried creating a mask layer not attached to the text layer itself, but that wasn't working either. I couldn't get the mask to hide or reveal anything.

Any help would be much appreciated.

Thanks,

Ray