Termites can't live in dry places and will not eat dry wood. Whatever you do keep your timber as dry as possible. Don't encase it in cob but leave some exposed (exposed to the inside of the house might be preferred) to allow a way for it to dry out quickly and breath.
They will burrow in tubes through anything they can in order to get at moist wood or they will surround dry wood and eventually it will moisten from the activity of the hive. I suppose a metal barrier will work, but just as well is rock or concrete. Perhaps use a concrete based mortar on your footing even if it's just a few inches of concrete/rock. If they can't physically burrow to the wood they won't be able to eat it and this mortar can be mixed with sand and clay. Your goal is a super-hard, rock-like layer they can't eat through. Unlike metal concrete won't rust away if exposed to a little moisture.
Chemical agents are a short-term solution. Look at railroad ties for example. They're literally soaked in heavy tar and chemicals yet when they stay moist they will rot or get eaten by termites pretty quickly. The other thing about chemicals is that they leach out eventually. I'm not saying not to use them, but I am saying that you should make keeping the timber dry and unreachable by termites the top priority. Chemicals will only help, they won't solve the problem in any amount.
Inspections would include looking at the bases of your footing for tubes coming from the ground. Destroy these on sight and chemically treat the area with whatever will KILL termites. http://www.hadleypestcontrol.com/assets/images/Termite_Tubes.jpg
Tubes likely mean they're eating your house not living in it. If you kill off the tubes usually that stops the problem, but they're persistent and will continue to try to find a way in. If you kill enough scouts with chemicals they will stop trying to come back after some time. Though it's not environmentally nice I've heard poring mineral spirits into their hole will do the trick. It destroys the chemical scent trail they leave marking your house as good eating and it kills a fair number of them at the same time. I only say that because I imagine you may not have good access to enviro-friendly alternatives out there.
Make sure the floors inside are sealed as well. If you want cheap flooring earthen tile would be do-able. Simply mix up clay/sand/concrete and tile the interior to prevent them from tubing inside. There are other options but the basic principle is to make something they can't physically tunnel through. Linseed oil is a typical way to finish these kinds of traditional floors.
Another thing to look out for is roaming colonies. You want to keep an eye out for colonies starting under the eaves of your roof. I would treat these yearly at the beginning of drone season, when you see termite drones flying around. That's your best hope of protection. Sodium borate, borax, salt and lime are all somewhat effective at deterring, but not killing, termites, but they do kill fungi, and kill plants and algae... Mixing all or some of those together (whatever is available) would make a decent preventative treatment under eaves and on exposed wood surfaces.