@Robert-And-Sarah0
The most straightforward way is to go to the calendar and simply block out the dates on the either side of your trip. You can block multiple dates in one go by simply selecting the start/end period for that action.
You could also, as an additional precaution, set your availability to the shortest window, which I think is three months in advance, but make sure to manually block a few weeks because of course that three months in advance will keep moving every day.
I hope that makes sense!