In some ways it is much easier to get access to a country than a mansion. Think about it. One person can sit in the middle of a mansion and have the chance to hear a door open, a window get busted, or Santa drop in through the chimney. One person can sit in the middle of a country and never hear another person; nevertheless someone swim onto their shores, fly in, or drive in. Thousands of people come into countries a day by land, sea, and air without anyone knowing. Add powers like teleportation, personal flight, cloaking, darkforce, shapeshifting, psionics, etc.