drainage

[bw]

I know this is not the right forum for this, but you guys are so smart i know i'll get a good answer. Any way this customer of mine wants me to fix this washout in his backyard. it's a slight slope that the water runs down to a picket fence and then into a pasture, it's a pretty ritsy neighborhood so it's got to look decent. It's washed out just under the fence, now should i fill it with gravel except about 8 or so inches fill with dirt, reseed and hope it grows fast or build a little retention pond and put a pvc drain pipe in the center and run it out in to the pasture behind his propery. any other ideas would be greatly appreciated. and thanks in advance