Drywood Termite repellent (external)
There are various wood treatment products that will help prevent termites from chewing on it and setting up a homestead. Many contain copper napthenate, which soaks into the wood when brushed or sprayed on. You asked how to "repel" them, and this works on wood. If you are looking to repel them some other way, can't really comment unless you more fully describe what it is that you want to do.