I'd be very careful trying to sterilize a pond's edge. One, it is not natural, two, big time possibility of water contamination. I actually put in many, many marginals in new ponds for poeple that don't like the bare rock generic look. And if I have a overgrown shoreline, I weed eat, brush cut and chainsaw. At the very end I may use some long term herbicide solution to finish the job, but only if I have to.
I might think of something to replace and crowd out the weeds that would look good pondside in the rocks. In places where I wanted nothing I would use a weedblock fabric.
