This time, strain them out as best you can. For delicate sauces, like hollandaise, add an ice cube to retard further cooking. If necessay, strain the sauce, too. For other sauces, try adding a little cream, then keep on cooking. Also, pay attention to the weather.
Sauces are more likely to curdle on humid weather, perhaps especially during thunderstorms.
Chill, skim off the fat, and reheat. Then, toss in a few ice cubes, wait until the fat congeals on them, and remove them. Blot the last bits up with paper towels laid on the surface of the sauce and reheat. Consider a sauce boat or pitcher in which the spout is at the end of a tube to the bottom, so that you are pouring the least fatty sauce directly from the bottom. Most gourmet or kitchen stores have such things.