Footing for arena? adding quarry dust to sand ok? anyone used quarry dust footing for their arena?

No it will harden. I think the best thing to use is sand. Its expensive but it lasts a long time and it is great, because when its wet it drains properly. I think if you call owners of beach's the might give you a good deal on beach sand. But it might have to many rocks in it. Go for sand, never dust.