If u can remove his shield it can be stacked untill 30k+ IMO. His skill Super Boulder can improve std attack 2x each round n Super Stone can improve shield too. Use Poison n Ignite for beating earth main ASAP.
With lightened boulder jutsu he can apply shield x2, and base don his resistance.. For instance at 4877 resistance I'm getting almost 2k shield so thats 4k shield every turn at 10 rounds... usually being that last thats 40k shield...