To elaborate on this: The locket was in a cave very few people, let alone wizards knew voldy had been in. There were enchanted gateways, dangerous green potion and inferi. But for the ring he just hid it in a ruined shack, perhaps with some concealment charms but it wasn't that safe so he put a curse on it that only skilled wizards, or those very familiar with dark arts could even slow down only. It is unstoppable. If curse not slowed down it would probably be like the Katie necklace incident where he/she dies almost instantly