The Modern Bodyguard
Peter Costerdine’s The Modern Bodyguard is an excellent research resource for realistic “executive protection”. Written in a typically sharp, slightly sneery British style, it delivers the blunt realities of the job, especially for civilians who lack both financial and legal resources compared to government personnel. For instance, it points out that private security, especially traveling private security, will almost always be unarmed for legal/political reasons (at least as of the time of writing).
It’s not perfect, and it says something about the type of genre that even Costerdine goes into tirades about various types of firearms. But its positives outweigh the negatives substantially. If you’re curious about realistic, limited-resource protection, I cannot recommend this book enough.