Warding Undead - adding partial effect to the Turn Undead roll

The cleric's Turn Undead effect in OD&D is an awfully binary affair. Even in the rolled range, the result is T or nothing.  Some drama could be added by having a close miss on the roll have partial effect. Here's a possible rule: A turn roll missed by one or two points give the effect W, Warded. The cleric's holy power is having some effect on the undead but it is still contested. While the Warded condition is in effect, undead attacks that just do conventional damage have it halved, round up and undead attacks that do drains have it downgraded to dice of damage. A shadow's strength drain or a wight's single level of life drain becomes a die of damage, a spectre's two level drain adds two dice of damage while warded. So there is still a fight on, but the party is protected temporarily from the scariest effect of powerful undead, their life drain. The warding effect emanates in a 30' radius around the cleric.

So, how long does warding last? That depends on how strong you want it to be and how much mechanics are worth keeping track of. The simplest answer is one combat round. Next might be 1D6 rounds, or a round plus at the cleric's next action, there is a new roll, that either resolves the condition or continues the ward. There could be rolls against WIS or CHA to maintain concentration each round, or when damaged by an undead, or other finer grained mechanics.

I think I would go with this: the cleric can maintain the ward until choosing to reroll for resolution or damaged by one of the warded undead. While maintaining the ward, the cleric can attack but not cast spells.