Okay, you were right. However, if you use too obvious of a Pokemon, they won't always switch to a Flying type. And plenty of foes use Earthquake remember, meaning you would easily be defeated. Alos, plenty of Pokemon have the Levitate ability. This strategy might work at times, but people know that when someone uses Dig, they have something planned, and as such will be prepared. Use this to find the Pokemon you think will work best if you still want this strategy:
Type in the moves you want then search for the Pokemon you think is best. You'll notice that Pokemon like Glaceon, Linnone, and Floatzel can learn Dig and Ice Beam. There are more Pkemon, but you might like these best.