Not always brother... Mahr is better described as a gift. Not always will it be a "security" in a worldly sense because if so why did the Prophet advice a man and woman to get married and the Mahr was that the man teaches the woman certain parts of the Quran which she didn't know.
Personally my Mahr was good enough for me cos I couldn't afford to buy all those books at that time! And in case my husband and I ever call it quits, May Allah protect us, I get to keep them all!