One of my favorites is "Husband, let me ask you -- what are your intentions regarding this marriage?"
You might also get deer-in-the-headlights, but I think it forces him to be a little more specific than the "work at it" one. He may, for example, a month and a half from now, in his DAM-ness say "Well, six weeks ago, didn't I invite you for a motorcycle ride? Wasn't that 'working at our marriage'??"
Puppy
Mostly I get I don't know and its one day at a time.
Then I would say:
"Then I will say this only once, (Husband). 'I don't know' isn't an acceptable answer for me anymore. If you can't do better than that, then I guess I HAVE my answer."
And then walk away, and forever drop the rope.
You've been at this WAY too long, Wifey. You deserve so much more.