This is the only cutter you will need....ever
http://www.cubancrafters.com/products.php/item_id/78
As you can see it has a stopper in the back so you cannot make a bad cut ever, this is the metal one for $15 or you can go plastic for $10
http://www.cubancrafters.com/products.php/item_id/5291
This is the one I have, and look it's only $6!!!!!
both of these have a lifetime warranty, so if anything goes wrong, just send it back and they will replace it.