We used fabric for lining a swale that we placed rock into. In less than a year there was enough dirt in the swale for new weeds to take hold in. Now we have weeds that come up through the gaps in the rock. They are easier to pull out because they are lightly rooted on top of the fabric, but still a pain. I would think the deeper you make the rocks (and if you use smaller rocks) the less likely you would be to get weeds with or without the fabric.
