Can you block the overflow that ends up running across your field so that it would run along the road edge or into the road?  Maybe it won't be popular, but if it causes a problem for them instead of you, it's a lot more likely to get fixed.  If that's not possible (or you don't want to really tick some people off) then I'd do some more complaining and/or tell them you're going to fix it yourself.  As long as you do it right, I can't imagine that they'll come out and remove it.  Then again, whenever a government entity is involved commonsense does not necessarily have to prevail.

Good luck,

Mike