Marg, the only thing I've done that worked to send them on their way was digging a hole, pouring boiling water into it, wait about 5 minutes, dig the hole deeper, pour more boiling water, wait, dig, pour, wait, dig, pour. I see you've said "boulder" not rock, so you likely can't move it in order to try this. :(

I'm pretty sure that now it's right under the boulder and all around it, there are also smaller ones popping up! Pretty soon I'll have to Duct tape my pant legs and hope that keeps them off me!

I have used diotomacious(spelling?) earth for mine - mainly because I have flickers and it`s not harmful to wildlife. You have to use it a few times to make a dent. The other product I use inside the house is Ant-B-Gone - it`s a clear, syrupy concoction. I put it on a little piece of wax paper and they suck it up, bring it back to the colony and feed to the rest. This would probably work quite well if you filled a container cap with it and sunk it ground level right by the hill. You will be shocked and amazed at how many belly up to the bar to drink their fill!

Borax and sugar works, just put the mix in an empty sour cream lid or the like and remove to water if around plants.

My front yard is infested with ant hills. I have tried cedar oil, DE, digging a hole into the ant hills and flooding it, destroying them with hose sprayer. Nothing works. These little buggers keep on going, and now they are in my side yard. Please help. Thank you.

I would give SouthCountryGuy`s recipe of borax and sugar a try - I don`t use it because of the flickers but I understand it is pretty deadly to them - start with one hill and keep at it - sometimes they pick up and move camp so you have to keep an eye out - I had a couple of those episodes this summer that were worthy of an Animal Planet special presentation - I dusted the whole 8 inch wide column with DE and that really knocked them back.