cutting ruler?
 

I forgot to bookmark a post about something that goes on your rulers that pushes the ruler down tighter for better cuts. Even keeps your hand away from the blade.

I think you are remembering a thread started by kimv44 on 12-2-12, and members suggested two products:
Slidelock ($28.95 for 14", $38.95 for 24") at http://quiltersslidelock.com
and Finger Guards ($14.95) at http://www.guidelines4quilting.com

I have both sizes of the Slice Lock rulers. I bought them more for safety but they work great to stop ruler slippage. They will fascinate most anyone who ask what is that? Wow, that's neat. LOL

Thanks it was the slide lock.