Uhh actually the CIA has a book about astral traveling you can find on their website, it goes over how to protect yourself before astral traveling in the beginning part of the workbook section. But as for day to day I think Jason Miller has 2 books on it, one is protection and reversal magick and I for the life of me can’t think of the other one, there’s also some squarespace website that has different lesson plans but it’s all pretty basic but if you want to check it out it’s
(It’s not a book just part of a lesson guide thing for beginners but it’s something

)
When it comes to protection I just use what I’ve learned over time so it’s not like a strict guide you’ll find in a book.
For instance here’s a thread I posted on how to make water for cleansing.
[Tutorial] - Updated Holy Water/Cleansing
When it comes down to it, I guess things on protection can be rather lacking because of the over saturation of junk you can find on magick, the gems get buried and not many people write whole books on strictly just defensive work. Or it could be that because what’s known works, and we all have our own defensive systems.
If you want any ideas,
You can use Sigils to create wards and recharge them after a set period of time, or you can choose a personal item crystal/pendent and lay your intentions into that while it’s laying on a sigil during a set moon/planetary phase that coincides with your own signs.
The overall theme with protection is, we all have different practices so what you choose for protection can depend on that. Some use the QC followed by the LBRP before each working. There’s also the reverse black mirror spell if you know someone is doing work against you.
I hope at least a bit of this info helped you in a direction that’s beneficial. Even if I didn’t name any books off top, the things mentioned may lead you to some lesser known idea’s or books that may have what you’re looking for.
When it comes to protection you can’t be too careful, but it’s not something I’ve ever obsessed over so I apologize for lack of better references. Defense is a pretty straight forward thing, be proactive about it and use what you find.
Hopefully someone will be able to give you a better book selection.
You can check out the WF library though and go through that to see if you find something that peaks your interest.