We have an outside cat and every year the ants try to get in her food. I finally found that vaseline smeared near the base of the dish kept them out. They won't cross vaseline. With no food available, they don't hang around.

We also get yearly invasions of ants into our kitchen. Since they come in a different way every year (darn them), I have to kill all the ones in the house and then stop them from coming in. The ones in the kitchen I kill with 409 and/or a paste of 20 Muleteam Borax. Neither is particularly toxic. Outside, I use an ant killer on their entrance point. That usually takes care of it until they find a new way in.