Have you tried instant grits? I have had partial success with instant grits. It's the swelling that occurs in their stomach that ends up taking them out. Other than that, I had em BAD when I lived in FL. I had to result to Bifenthrin based chemical to eradicate them. I would suppose you could coop up your chicks, spray very liberally and put pavers over where you sprayed to keep the chickens out of the soil. It has a stay time of roughly 3 to 4 months. It is a neurotoxin to insects and most effective on ants, cockroaches and related bugs. It is supposed to be harmless to all vertebrates and I have seen no ill effect in its use. I continue to use it to treat as a trenching barrier for the home. You can try organic, but fire ants have been the most persistent of pests I have ever experienced.