All good ideas so far Tom . You might find this video interesting of what an ant colony looks like underground . Granted this video are ants of a different varity and far more of a problem then you have , but it will give you an idea of why its so hard to destroy an ant colony plus the fact that they reproduce so fast .
I have been fighting carpenter ants for years ( Our large 100+ year old trees are full of them ) that have been here since before we got our place and theres only one sure fire way to get any control over them , Diatomaceous Earth (DE). I will post a few links as to what it is and its many uses but it will rid you of perty much any insect problem you have if applied correctly . Its best to use a mask when you use it so the dust particles dont get in your lungs though .
There are several pesticides that have it in their ingredients but its much more expensive packaged that way then you can buy it online . I buy it in bulk 50 lbs at a time and use it all over the property as well as in and around the house for spider control . Good luck on getting them under control .
From wikipedia .
http://en.wikipedia.org/wiki/Diatomaceous_earth
Pest control
Diatomite is also used as an
insecticide, due to its physico-
sorptive properties. The fine powder absorbs
lipids from the waxy outer layer of insects'
exoskeletons, causing them to dehydrate.
[9] Arthropods die as a result of the water pressure deficiency, based on
Fick's law of diffusion. This also works against
gastropods and is commonly employed in gardening to defeat
slugs. However, since slugs inhabit humid environments, efficacy is very low. It is sometimes mixed with an attractant or other additives to increase its effectiveness. Medical-grade diatomite is sometimes used to
de-worm both animals and humans, with questionable efficacy.
[10][11] It is most commonly used in lieu of
boric acid, and can be used to help control and eventually eliminate
cockroach and
flea infestations. This material has wide application for insect control in grain storage.
[12] It has also been used to control
bedbug infestations, but this method may take weeks to work.
[13]
Interesting reading as to its other uses .
http://www.wolfcreekranch.net/defaq.htm
Where to buy online in bulk .
http://www.google.com/products/cata...a=X&ei=Gm4lTv6gBYSssQLEm4jYCw&ved=0CFgQ8wIwAg#
[ame="http://www.youtube.com/watch?v=W6d5pcr4X30"]Worlds Biggest Ant Hill AMAZING - YouTube[/ame]