Boy, can I empathize with your situation. Last week I was kneeling down to "tie up" the base of a plant. I felt a pinch on my arm and it was 1/2" long ant. Then I noticed that my knee was inches from an ant hill and there were 50-100 ants moving up my thigh; many already on the back of my tee-shirt.
What worked for me was a can of Wasp & Hornet spray (don't remember the brand). First I shot it over the general area of the ant hill (since the hill was still covered in ants). Then I dug into the hill with my planting knife to get below the surface and doused that heavily. Broke the ground a few more spots (the hill itself was about 8 inches wide) and doused. Ended up using up the entire can of spray.
Haven't seen an ant there all week. But -- WARNING -- I have know idea whether or not the product is safe for dogs. These plants are in an area outside of my dog's area, so I knew she wouldn't be exposed to it.
But it really worked.
