I feel like not wanting to have a sentence countered is sort of antithetical to the spirit of the game? That's the way you refine it to its particulars.
It can still be powerful even as a +0 sentence, because you still would need a suitable Means to counter it - and even countering it don't end it, just stops it for a situation. And then the players/characters wouldn't necessarily have what they came to the Moon for, so they'll still have to come back in and re-engage with the situation.
(And if the goal is to permanently break the loop for everyone on the Moon, a +3 sentence only needs to be Countered 3 times before it's retired, vs at least 12 attempts if it's at +0.)