There was a time when bibles were chained to pulpits and armed guards watched over royal libraries. But there were historically more subtle ways to discourage theft. A fascinating report from Atlas Obscura reveals popularity of curses.
A good curse can go a long way to putting, literally, the fear of God into any would-be thief. Just try writing a little ditty like this on the first page of a treasured tome:
“For him that stealeth, or borroweth and returneth not, this book from its owner, let it change into a serpent in his hand & rend him. Let him be struck with palsy & all his members blasted. Let him languish in pain crying aloud for mercy, & let there be no surcease to his agony till he sing in dissolution. Let bookworms gnaw his entrails in token of the Worm that dieth not, & when at last he goeth to his final punishment, let the flames of Hell consume him for ever.”
That should do the trick.