The Swiss were the first to institute mandatory military service from every able-bodied male citizen. Later, Israel adopted the same model. They also have engineered their nation to collapse all roads going into the country as a defense mechanism. The Swiss are completely willing to do whatever it takes to make an invasion tiresome and difficult for possible invaders.
They've also planned on making that hypothetical a particularly deadly one. Where a highway bridge crosses a railroad, a segment of the bridge is programmed to drop on the railroad. Primacord fuses are built into the bridge. Hidden artillery is in place on either side, set to prevent the enemy from clearing or repairing the damage.
For a nation legendary for it's militant neutrality, those sort of fortifications are probably crucial. As a nation that maintained neutrality since 1815, through dozens of European wars, two world wars, and the Cold War it's important to have a very secure insurance policy against overeager invaders.