The Ring of Saruman?

[Gurthang]

Perhaps Saruman's Ring did work, but not that made much difference to the story. One aspect of the One was that Sauron had a controlling power when he possessed it. Not just over those in opposition to him, but to those already under his authority. He used his Ring to drive his armies before him, and with its power they were less fearful and more aggressive towards their master's goal.

Saruman's Ring could have done this. With his army of Uruks he needed an easy way to control them, since Orcs do not take orders easily. His Ring may have given him the will-power to command them. Perhaps this is why they were so swift and tireless and could move in sunlight. 'They run as though the very whips of their master were behind them.' Saruman's Ring could have been able to branch out and push his servants even beyond his own physical reach.

His Ring provided him with increased 'persuasive' power, not just over others but even more importantly over his own troops.