The only way you can prevent weeds from growing on soil is to cover it all with a weed barrier and only cut holes where you plant your vegetables or anything. Some weeds will even continue under the weed barrier (like bindweeds--I found roots of bindweeds 2 yards long under the weed barrier). Weeding is part of gardening---When you had it tilled up, some of the roots may be cut into small pieces. They in turn could also become new plants. You could use Eraser and kill all the weeds that were there so you at least are sure there are no small roots of bindweeds, mugworts, and Bermuda grass. Wait 2 weeks---then cover with the weed barrier and just plant in the cut holes. If there are any soil above the weed barrier, some weeds will find the soil and grow there- I think Mother Nature thinks if there is bare soil, something has to grow on it----