The best way to stop weeds really is dependent upon where you are trying to stop them. For example, if you are interested in stopping weeds between cracks in a sidewalk or driveway than a chemical such as round up could do the job. If you are trying to prevent weeds in landscape conditions than the best method is using a mulch. There is no way to 100% eliminate the job of weeding but mulch is probably the best way to do the job on a larger basis.
 

Here is a link to an article on Natural Weed Control 

http://www.bloomingsecrets.com/featured/the-basics-of-natural-weed-control