Look at the Swiss. They have set up tank barriers and heavily fortified artillery all over the country. The Swiss Alps are basically one big fortress. All across the place you can find buildings looking like houses at first sight, but which turn out to be heavily armored artillery positions, especially at landscape gaps near the border. You can’t cross with tanks because of several rows of concrete teeth hiding in the vegetation, and the only road passing through runs through at least three or four targeting areas.