You can purchase beneficial nematodes from your local feedstore for long term fire ant control. They are micro organisms that kill ants and create competiton for them. It's all natural and won't hurt anything but the ants. Here's a link...
I have used it and still do use it because 1 month ago my place was infested with ants. I have a little over an acre and it was like one big ant bed. I've done 3 treatments so far and there are only a few small beds left. I decided that with my budget I could afford 6 treatments this year, one per week over a 6 week period. You may say that's too much, but I'll only have to do 1 or 2 treatments a year after I get them under control. In the long run it is a very inexpensive and extremely eco-friendly way to control pests.