Melissa Mortensen of the pollka-dot-chair had cut her finger, quite badly, with a rotary cutter and had to have stitches and everything JUST LIKE ME!
Which totally blew my mind because I thought I was the only one who was klutzy and cut their finger practically off with a rotary cutter. After it happened I wondered why I didn't see it coming and how could I prevent it from happening again.
Well one way to prevent cutting your finger when your rotary cutter jumps the ruler is to QUIT using a rotary cutter and ruler. Not going there!
So, I found a couple of gadgets that I started using. One was a little suction cup handle that hooks on the ruler, ok but kind of flimsy. Another is a little L shaped stick-on ruler handle that the manufactures sell. They protect your finger but can interfere with your ability to see the ruler markings.
I also read that some people use the suction handle that you can buy to help you in the bathtub. Since I have not used that, I can't comment.
The best solution I have found is the quilters slidelock. Here is one place you can purchase it. However I have not gone shopping so, you might want to look around. They also have a link to a demo video.
I like my slidelock (I purchased it at the 2012 HMQS) It not only protects my fingers, it does a great job of keeping my ruler in place so my cuts are much more accurate. I like more accurate because things go together smoother when they are cut accurate. And then LESS UN-PICKING!! Which is always a good thing :-)
It took years for my finger to feel normal again. I am happy to say that it feels fine now and the nail grows mostly normally too. I suggest that you take good care of your fingers and use a protective tool with your rulers.