Where in the world are you? That may well make a difference in what is recommended.

kimmq is kimmsr

michigan

What kind of rocks? Like natural rocky outcroppings or like a mulch of small stones that you put there? There are chemicals you can buy that will sterilize the soil for a number of months so that nothing can grow there, but it's really nasty stuff and not something I would want to introduce onto my property especially in such a large area.

What is the stuff? The rocks are about 3" x 3" or slightly bigger, and some large ones. Some smaller ones mixed in. It's a lot of different sizes. They roll off it you step on them.

Something like this:
http://www.domyownpestcontrol.com/tvc-total-vegetation-control-p-2116.html

Please do your research before using something like this. I have not ever used it myself, and I only mentioned it because you specifically asked about making the soil ungrowable--this is not something I would personally use anywhere that humans or animals could come into regular contact with.

I suppose you could also try a groundcover. There are creeping sedums that will grow over rocks, but for such a large area it would take forever for a groundcover to establish. Even then, it would cut down on the weeds but not eliminate them entirely. You could also strategically plant trees to shade the hillside--also not an immediate solution until the trees matured but it would cut down on the weed pressure.

Thank you, ajs317. I've thought about wide junipers to put on the hill, but I'm not sure what I want to do yet.

If you actually have space to dig and plant a root ball, creeping juniper could work and will expand to cover a larger area. Those grow very slowly though, and once you have that or some other groundcover planted, you obviously can't spray herbicide (even more run of the mill ones) to control the weeds that pop up between the plantings.

Yes, I thought of that. So I was thinking the real thick (like 2 - 3 foot high) junipers. There are so many different kinds. My friend has some 6 foot wide by 3 foot high and nothing grows through. Maybe I'll experiment for awhile.

We are not in MI, but on a very steep hill. Nothing stops weeds, but junipers will keep your hill from sliding, and weeds don't like to grow under the shade of junipers. You could make gin with the berries! Woo Hoo!!