Unfortunately, green doesn't have much in the way of disruption / Counter magic. Just doesn't fit in the color pie. So you're kind of forced into artifacts. The only thing that really comes to mind are prison cards like
Defense Grid (doesn't really stop it altogether, but can make it a lot harder for them to get through),
Trinisphere isn't as good and cost more cash, and a
Chalice of the Void on 2 (super pricey but overwhelmingly powerful).
Ok, so while trying to come up with Artifacts I thought of some options in Green that sort of gets you there.
Plow Under is just super good as you can put the two land they would use to cast their
fog effect on top of their deck, and now instead of drawing any gas for the next two turns, they just redraw their lands. You'd have to have an insane amount of mana to do it all in the same turn, but
Plow Under is a sweet card at any point of the game.
Finally, a creature sacrifice outlet like
Greater Good or
Evolutionary Leap could save you from dying to
Batwing Brume (while it's on the stack, sacrifice enough creatures to avoid dying to the trigger). The nice thing here is both cards are kind of cheap (
Leap more so than
Greater Good), and work wonderfully in a creature heavy Overrun-type deck since they refill your hand.
Greater Good is especially good here since sac-ing creatures with
Overrun on them gives you an extra three cards per creature anyway (and the sacing itself costs no mana).
Hope this gives you some ideas! Good luck