Masking tape works—if you flag it
There's nothing new about using masking tape on a bit to indicate drilling depth, but it can be difficult to tell when that tape sleeve hits the workpiece. And if you go a little too far, the sleeve tends to slide up the bit, making subsequent holes too deep. Rather than simply wrapping the tape around the bit like a sleeve, stick the loose ends together to form a flag. When the flapping flag wipes away all the sawdust around the hole, you've hit your depth mark.
—from the WOOD® shop