Horse should not have time to paw at ground in the first place. And to me worst thing to do is to have horse close to you, which means you have to move if one acts up, rather than being able to make them move.
Horse is running this show, get after him and make it count if you need to, and that means using whip to pop that rear if you must.
If you don't get this fixed? It will trickle over into every single thing you want to do with horse.