"Never lend books, for no one ever returns them, the only books I have in my library are books that other folks have lent me." Anatole France.
I have no idea what kind of friends Monsieur France had but I don't agree with that. At all.
Alright, you have to look a little after them. I write it down when I lend a book to someone, who when what. That's all you need. Then a little reminder if it hasn't been returned after a while. Most people don't even forget they have your book, they just forget to take ti with them the next time they see you.
I have only once lost a book. The colleague I had lent it to point blank refused to admit I had ever given it to her. Needless to say, that was the last time she saw one of my books.