Hi -
Eric's way is the best automated way but some things to consider with that...
If you do this, you do not see the grey thingy (the technical term) in the scheduling tool that you do if they take off. You will see them over-allocated for the week but there isn't a visual indicator. This is important because if you have multiple people on tasks, a person might have a task due on Friday even if they aren't supposed to work. This is because your options for settings are task owner's schedule or project schedule. Our resource managers have found the grey things helpful so they can contour the task and avoid the "day off" for that resource.
So, in conclusion, a schedule is the best automated way, but we have found some grey benefits just giving the person every Friday off in their time-off. Just depends on the tools and way you resource.