Don't ever use ROUNDUP on weeds in your yard or eat foods sprayed with it.

http://articles.mercola.com/sites/articles/archive/2012/03/13/active-ingredient-glyphosate-in-roundup-herbicides-found-in-peoples-urine.aspx?e_cid=20120313_DNL_art_1

The "Safe" Garden Product that Can Destroy Your DNA

EXCERPT:  It's important to avoid the use of Roundup on your lawn and garden, but on a larger scale the best way to fight back against this chemical is by boycotting the GM crops that were developed for its use. Several organizations, including Mercola.com, the Organic Consumers Association, the Institute for Responsible Technology, and the Environmental Working Group, are working to generate a tipping point of consumer rejection to make GMOs a thing of the past.

Here's how you can get involved:

• If you live in California and are willing to attend a short training session and then start collecting petition signatures (you will be part of a team of 2-4 people) for the California Ballot Initiative, sign up here. (For more information see: The California Ballot Initiative: Taking Down Monsanto.) Also remember to share this information with family and friends in California!
• Whether you live in California or not, please donate money to this historic effort
• Distribute WIDELY the Non-GMO Shopping Guide to help you identify and avoid foods with GMOs. Look for products (including organic products) that feature the Non-GMO Project Verified Seal to be sure that at-risk ingredients have been tested for GMO content. You can also download the free iPhone application that is available in the iTunes store. You can find it by searching for ShopNoGMO in the applications.

In the meantime, the simplest way to avoid GM foods is to buy whole, certified organic foods. By definition, foods that are certified organic must never intentionally use GM organisms, must be produced without artificial pesticides and fertilizers and come from an animal reared without the routine use of antibiotics, growth promoters or other drugs. Additionally, grass-fed beef will not have been fed GM corn feed, although now that GM alfalfa is approved, grass-fed will not always mean GMO free.

You can also look for foods that are "non-GMO verified" by the Non-GMO Project.