[Z06vette]

That's fair amount of slope you have there. Sod would have been my choice as well, as grass is one of the best erosion control measures. There really isnt much you could have done if it was just laid. Once the grass starts to root in, you should not see much of any wash from under it. Using sod staples will help hold them in future rains until it roots, but nothing will really stop the washout from under it until that happens. Once you re-grade the slope & set the sod back down, you could use some hay or pine straw bales where the grass meets the concrete. Run them the entire length & drive some rebar through them into the ground. This will dam the water so it doesnt rush under the new sod. Put as much of the bale on the concrete as possible & still leave enough to get the rebar through. That way it wont kill the grass. Just be sure you dont flood another area with the bale dam. In a few weeks the grass should be rooted & you can remove the bales. Sorry for the long reply. Hope this makes sense.
Scott