Obviously sat-nav guided systems should not rely on unprotected satellite navigation alone. You need complementary systems. EU's GNSS has PRS (Public Regulate

Obviously sat-nav guided systems should not rely on unprotected satellite navigation alone. You need complementary systems. EU's GNSS has PRS (Public Regulated Service) is authenticated and can be used in sensitive applications for civilian uses. US has GPS modes that are protected but they seem to be only for military. There is also Wide Area Augmentation System (WAAS) and European Geostationary Navigation Overlay Service (EGNOS). They augment GPS/Golnass and Galileo and provide integrity and more accuracy. Typically new sat-nav systems have multi-constellation capability and they can receive from from GPS/GNSS/Golnass. Even new smartphones have that capability. Of course, if all of them are unprotected, you can spoof them all parallel.