Many years ago I was talking with a greenkeeper on how they control ants and he said they use lawn grub chemicals.
He said liquid concentrate is similar to ant sand/ant rid, but the liquid concentrate of lawn grub killer is a lot cheaper. So now I just mix it up in the watering can and pour it over nets I find in the yard.
But you have to remember black ants can travel along way, so while you might clear all the nets in your yard, they could be coming from your neighbours yards or even living inside a brick wall where access to use chemicals is difficult.