Damn noisy frogs!

I've got a pond about the size of a large swimming pool. Deepest point is 12'. The frogs at night are incredibly loud and I want to quiet them. Disturbing the water, (throwing firewood into the pond), quiets them, but you can see there problem with that. I've yet to try coffee grounds around the perimeter. I hear that the coffee irritates their skin, thus making them vamoose.
I don't want to kill them off.
Any ideas? Please?