Doktor Doom
I had a bit of an ant problem last year.
Find where the little bastards live and cover it with this stuff.
$25/can, but it was the 4th ant killer I'd tried (tried everything that you can get at Home Depot etc, that says Ant Killer on it....none of them work)
Had this recommended to me by a a professional gardener...works awesome, but you have to find the nest, dig it up and soak it.
Regards,
Woodguy