One problem I've seen a few times in my game is repeated attempts to turn undead when it has failed.
To paraphrase one of my players, "You don't really know it won't work until you've rolled a 3 and it still failed." That attitude can be inspiring, but it's also a stubbornness that can grind down a referee's soul. It's painful to watch someone roll and fail, roll and fail, roll and fail, hoping that eventually they're roll low enough and you high enough to let those damned undead just run away (or suffer a penalty).
That's especially the case when the PCs are attempting to turn undead when it flatly won't work - the enemies aren't really undead, the enemies are in a special zone where they cannot be turned (a very D&D thing, but also something I've used), the enemy has enourmous effective Will and winning the contest is either unlikely or impossible. Yet turn after turn the PCs start to pin their hopes on a good roll instead of having the cleric or holy warrior do something else that can actually help.
It also means the drama of that first Turn Undead roll isn't. It's a question of, "Can I beat them this second? No? How about this second?" A lucky roll by undead foes just spares them for a second.
Perhaps ironically, I think a way to help players out of this trap, and get the GM out of the "fun" of a good roll for an undead foe becoming just a one-second delay of the inevitable with a penalty.
I think a limitation helps both - the player knows to stop trying and do other things, not just pray for a good roll or think he or she is helping when they just are not. It also means a good roll - or a well-used Wish or a Luck roll isnt just sparing the undead for a second.
Here are two options. I am leaning toward the first one for use in my own games, but I might use the second if it sits well enough with me after further thought.
Cumulative Turning Penalties
For each attempt to turn the same undead, you roll at a cumulative -2 penalty. This penalty lasts for 24 hours from the last turning attempt.
One Try Per Day
If you fail to turn a specific undead, you will automatically fail in any attempt until at least 24 hours after your last turning attempt. If you succeed, and stop concentrating on turning, you may try again - but if you fail on a subsquent turning, you cannot attempt it again for at least 24 hours.
"Surely a 3 must do something special?"
That logic is too combat-and-skill-roll oriented. It's not for Quick Contests. You really need to drop the thought that a "3" is anything better than the biggest margin you can succeed by. If you rolled a pretty good roll and failed, hoping for "critical" isn't a good approach when the rules that apply don't have critical successes.
Why -2, not -1?
-1 would make sense, much like forcing doors has, but it comes with a 1 FP cost for repeated efforts. This comes with none, so if you have a reasonably high roll (especially one of 17+ so you're already capped by the Rule of 16) there is little reason to worry about a -1. A -2 adds up twice as quickly, and makes attempts past 2-3 times crippling for all but the best of clerics against the worst of undead. There is still a chance, but each try is less and less likely. I think -2 works pretty well. So would -3, but I think -4 seems a bit too much.
Which one is for Felltower?
I'm a bit torn . . . I'm leaning toward the -1 cumulative but "One try per day" is harsh and easy. The first ignores failure or success - that penalty comes up even if you succeeded but then let the turning lapse. The second just says no.