First follow all the suggestions about removing wood, making sure no dirt contacts wood, etc.
Also, take advantage of the free termite inspections from several companies (you wouldn't believe the different reports you'll get from different companies.) You'll learn useful stuff about your particular situation. Our inspections didn't see any termites in the building, but of course they can be there for years without a sign. And they can get in a spot smaller than a pencil lead. We knew we had them right outside the house though, from some cardboard we had put down for mulch.
Find your termite colonies by putting damp cardboard down. Look under there every so often. They'll be more than obvious if the termites found it. Moist areas, areas with wood (like old tree stumps) and so on are more likely. (Although I wonder if they'd bother with my cardboard if they had a well-rotted tree stump?)
We bought Termidor SC for 20oz. Costs $60 but it makes I don't know how many gallons (about 2T per gallon.) Took large coffee cans, filled with cardboard, soaked with the diluted Termidor solution. Sealed & locked while it was absorbing.
Then took other coffee cans (the 3# size) and punched a bunch of holes all over except the top 3" or so. Put the soaked cardboard in them, put the lid on and taped. Buried them where the termites are, with the lid about level with the ground. We also put a piece of soaked cardboard below the can, just to entice them to explore that can. Covered the lid with a big rock. The area will be more attractive if there is some moisture (we live in the desert) and they'll tend to find it. If you've identified the areas the colony is in, though, it shouldn't be hard to get them to find the cans.
Within a month or so the termites should find it, eat it, and take it home. You can look through the lid to see if there's any activity. Within 3 months the colony should be dead or close to it, if you've fed them enough poison. (Use a few cans to start; you can get an idea after a while. If they're eating all the cardboard, give them more cans.) It's a biological poison and they don't get sick immediately; it gives them time to get back to the colony and spread the poison with their grooming habits. Hopefully it will get as far as the queen.
My best guess is that one bottle of Termidor will last for years if we keep on top of it. Colonies start and grow; if we can catch them when they start we can stop them. I think. And termites are vitally important in the ecological scheme of things; it is just the colonies chomping at our house I want to interfere with.
A. This is serious poison. Use outside, be very careful, use gloves, eye protection and masks, work slowly and carefully. Send the kids to grandma's. Read all the directions about not using near waterways and stuff like that. Rinse according to the directions and throw everything away carefully. Lock your supplies, your soaking cans, and all that.
B. This is just what we've done. There are no guarantees. This is not an approved use of Termidor. If you do this then you are responsible for any injuries.
For dry wood termites, boric acid is probably the best. I think a liquid spray would be better to adhere to the wood even after it dries, especially if there is some sort of thing you could put into it to help it adhere. Or soak sawdust in boric acid (or just mix it in?) and put it in the wall cavities... I just think termites would like sawdust better than chomping into hard wood... Its one reason why I used cardboard instead of pine boards. As far as boric acid, I buy it at the dollar stores. The quantity isn't large, but all I've ever used it for is to keep a line of dust in the crack outside of the exterior doors, and it goes forever used that way. (Mostly to prevent cockroaches and ants, which it does.) Worth price checking anyway.
Some pest control companies use Termidor by drilling holes every 18" or so between studs around eye level more or less, and they have special equipment that sprays all around inside the studs, then they caulk the holes. I wouldn't try anything like this; goes way past my safety standards since we have no training, no right equipment, not that kind of safety clothes. I might be willing if a wall was already opened to dilute the Termidor, paint it on the wood the termites are already eating, and close it up. Although in that case the boric acid would do just as well, and be less toxic. ... View related article.
