I got this one from Mike Tuchscherer. If you want to eliminate dropped Deadlifts, the best way to do it is with static holds. During your last set of Deadlifts, regardless of however many sets you do, when you stand up with the last rep hold it for as long as you can. Do this every time you Deadlift and your grip will develop quickly.
It’s not hard to see why this works so well. It’s literally the most specific way to train your grip. You might not be able to hold it for long, at first. Each time you Deadlift you should be able to hold it longer than the last time. I’ve tried other methods of working the grip including Captains of Crush, etc. Nothing seems to work so well as this.