Volunteer small grain in soybeans

I'm getting frustrated with the amount of volunteer oats I'm getting in my double crop beans. I have already made 2 separate applications of roundup and I thought that would be all of it. Well I went and looked at my beans today and there is another flush of oats coming up......I sure hate to drive over these beans again since they are waist deep and will knock a bunch down but I don't guess I have any choice. What could I have sprayed to give me residual control of the volunteer oats but allow me to replant oats or wheat after soybean harvest in November?

Volunteer small grain in soybeans