Even by buying certified organic rice. Pollen blows in the wind, transported by animals and insects, contaminates an organic crop, and unless one does a DNA analysis on your rice, you won't be sure. Certainly, you might get some signs, differentiation in size and color, but frankly most of the holders of USDA organic certification are corporate farmers, and they'll take a look at the rice, shrug their shoulders, and harvest the rice for profit.
And frankly, if Bayer, or the farmer suspects that their GM crop has contaminated an organic or non GM operation, they will sue to have the crop destroyed, and win. Another method of driving small farmers out of business.
And frankly USDA certified has become such a mess, hassle and expense that many small organic farmers are foregoing the label. In fact the certification label was designed to favor corporate farmers, no the small ones. The expense is prohibitive, as is the record keeping. Doing the research for compliance factors is time consuming and confusing, as is the list of materials that one can use on the crops. Corporate farmers have the money and manpower to pull this off, thus they can look green while continuing to kill farmland. Meanwhile, the small, concientous organic farmer can't afford the certification, or worse yet has his application denied over some obscure BS that he didn't catch in all the legalese.
Better than USDA certified organic, look for the Certified Naturally Grown label. Designed for small organic farmers, and actually more reliable than corporate organics, you'll find CNG at your local farmers' market. Support small farms, buy local, buy CNG.<
http://www.naturallygrown.org/> And whereas a certified organic operation would probably allow GM rice to slide on buy, CNG farmers won't. They not only pay more attention to their crops, and care more about their product quality, they also care more about their customers.