Jimmy:
Many liquid dishwashing soaps contain anionic surfactant, and only a relatively small amount at that. Some folks use these detergents for your stated purpose, but the glyphosate's performance certainly isn't maximized by doing so. Nevertheless, it is probably better than using nothing in conjuction with the herbicide.
Many farm supply stores will carry some type of agricultural surfactant (non-ionic), but you should verify that their product may be safely used in aquatic sites (many cannot).
Otherwise, you should be able to obtain an appropriate surfactant from the same source that sold you the RODEO, AQUAMASTER, or any other brand of aquatic-labeled glyphosate.
KD
