How thick should you lay River Rock?

If you are using the river rock as veneer most will come in around 4″-6″ thick. Smaller and you start to get more into the pebble area of rocks.

If you go more than 6″ thick you might as well construct the wall out the rocks as tying to a wall starts to get tricky due to weight. Seriously, if you don’t know what you are doing with large rocks you can collapse your wall.