If you're using an ant killer from one of the big box stores, it most-likely is weak and washing away. I suggest looking around doyourownpestcontrol.com or domyownpestcontrol.com and finding both a sugar-based ant bait, as well as a protein-based ant bait. Baits are important, because the ants will carry it back to their next and kill the colony. Now, understand that you won't see instant results from a bait, but in the end, they'll do much better at telling the ants they're unwelcome. Most spray ant killers are generally regarded as safe, once they have dried, so pets and children should be OK. Some even have a residual affect if they are properly applied. Make sure that you don't apply the big-box store "insect barrier" products near the baits, as the "insect barrier" stuff contains a repellant, which will prevent the critters from taking the bait.