Question
what is affordable that will keep the weeds out of a gravel driveway?  If it sterilizes the soil,,good!!

Do you know what kind of borate they used as fire retardent in fighting forest fires?

Bend, Oregon

Answer
You can buy weed-and-grass killers at garden centers or home improvement centers which are used for driveways / patios. These particular weed killers are based on sodium (salts) and will stay in the soil so nothing will grow for about 6-12 months.

There are various types of grass killers. Some will only kill grass that is actively growing and will not stay in the soil. Others, like the onces explained above, will stay active in the soil. You want the latter; and usually the lable states that they are for patios or driveways.