frog leaps in
water's sound.
Why not two possessives? Can't the pond, as central fact of the poem's occasion, be the source and the generation of the water's sound as well as of the frog? The environment--i.e., the larger locus of the poem's activity-- may very well be the source of this poem's meaningfulness, so I thought I might give the sound it's generative location in the pond itself. I do dig the enjambments quite a bit, whatever the case may end up to be.
