Termidor works great... I trenched it out about 4-5 feet circling the pens... No ants..No anything for that matter....It's used primarily around here for perimeter termite control .... Lasting up to 10 yrs on one treatment.... Pest control people told me its pretty much harmless to pets once it dries....
First time I used it I sprayed some on a rather large active fire ant mound... Next day there was no activity.... They either died or left..
Remember to mix it as recommended... Expensive but very concentrated..