Boric Acid: Mix this with some cocoa powder, flour, or other powdered food (I use sugar) and it helps kill anything with an exoskeleton. Boric acid is a 100% effective method since the acid eats the body of the insect, and they can never become immune to that! It isn’t instant. You just need to put the powder where they walk. Boric acid becomes ineffective over time, so it needs to be re-applied periodically, and water makes it lose potency, so using it outdoors isn’t as effective.
Menthol Scents: Eucalyptus, Peppermint, tea tree, basically anything menthol related will help deter ants. Use a small brush to spread the oil where they are getting in, and be sure to clean up their scent trails beforehand.
Cayenne Pepper: Another scent that ants despise, sprinkle this around where they are getting in as well.
Chalk: Ants supposidly will not cross over a line of chalk. If you are able to outline where they are getting in with chalk, this should help keep them from getting in your home.