In my limited experience the rocks/stones do not stop weed growth, in fact, they may make control a lot more difficult. Plants will grow anywhere they can reach water and/or dirt.
If you go with stone, a shelf to start as a base will help the slumping, start with a row of large ones. I would suggest making it twice as wide as you think necessary. I started mine at three feet deep and made it three feet wide.
Alternately, you might look at grasses or other types of ground cover that will compete well with what weeds you have. One key to weed control is to cut them back before they seed, slow, but effective.
Pursue the question about how you are going to put the stone in place, my pond is small and it was a large project.
Some one here used a fabric cover to hold the erosion down and help with the grass/ground cover start up, Cecil? Burlap, I think. If you are redoing you pond you might be able to plant low and before it refills.
