Like a lot of things, try drawing them in to attack you at a river crossing. That way, you can engage the elephants with your artie without having to worry as much about their infantry overrunning your guns.
I fought off a Timurid stack that had no less than 10 units of elephant artillery that way.
And if they ever get within range, ribaults can just destroy elephant units. I fired one into a full unit of elephants once; one firing slew half the elephants and routed them.
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