paul--
Once you get past 2 hours you're down to the high singles, past 3 hours your down to less than 2%--actually less, probably more like <1%. Your sauce does not need to boil for the duration, just simmer. Alcohol evaporates at 172 or higher.
If any alcohol is a concern there are a couple things you can do. One would be to simmer longer than 3 hours (bring to a boil first, then reduce to a simmer); the other would be to simmer the alcohol portion of the sauce first, separately, then add it to your sauce. How long you could simmer it alone would depend on its original volume.
Alcohol (the actual alcohol component of spirits) is not a concern to me, but for other reasons (taste, primarily) I do not cook sauces for extended periods--even tomato sauces for pasta. But, were it a concern, I would note that usually the spirits component of a sauce (with a few exceptions) is already small to begin with, and the alcohol component of the spirits smaller still--even before cooking. Cooking, even for a brief period, will reduce the alcohol component further yet. But if you want virtually no alcohol to remain you'll have to cook it for a while, either in the sauce, separately, or both.