I used 2" lateral rock (crushed limestone) to reduce bank erosion, but had the normal 3 to 1 slope. As you can see in the pictures below, it does not stop weeds. I think your idea would work until enough silt and sediment filled in between the rocks, then the weeds would be there. Might take it several years though. Just my guess, as no personal experience with what you are trying to do.
On the slope, to get the rocks to stay in place, I run the front of the loader tractor down the bank, angled the bucket so it dug into the bank, and pushed a ledge of dirt for the bottom of the rock layer to rest on. I also did this in various places deeper to make rock beds for spawning, if the fish so chose to use them. Some I then covered with finer material, some not. Just what I did, in case the ideas help.
The pictures below are of another idea a person can do with a big rock. My wife wanted a nice rock to set on as she did her morning walk around the pond. She wanted a rock the size of a pickup truck and I had to explain how much a rock that size would weigh and the logistics of moving and handling it. She settled for what is in the pictures. The big sandstone actually has some history on our farm. It was likely quarried around a hundred years ago from a sandstone hand quarry less than a mile from our house where a lot of local foundation rocks came from back in that day (sandstone for foundation, ashes and salt for mortar). It was the cornerstone of the west addition to our 1900 era barn, probably put in a few years after the main part of the barn was built. We took it out when we put concrete in its place when we fixed the rotted out portion of the wall. So it has some nostalgic value to us also. The water is about 20" low in the pond at the time we put this in. Below what you see in the pictures used a backhoe to dig out down to solid clay in the dam and put in a 4' diameter concrete foundation so it is not going anywhere. At full pool water will be a couple inches below the bottom of the big rock. When pond is full, will mostly just see the big rock from the water side. Water runs underneath it. Need to get a picture from that side.
