I've been very successful with boric acid. It isn't non-toxic, but it's much less toxic to mammals than some of the other insecticides, and you can keep it in corners and crevices where pets can't get to it. The "nice" thing about ants is that they follow their little trails, so you just have to cross their path with a line of boric acid, and they don't know enough to go around it. Follow their trail to their point of entry from outside, and treat that, too.