We, Reform Jews, consider it sufficient to place a single Mezuzzah on the main entrance door of the home and do not require Mezuzzot on the other doors. We need to place a Mezuzzah only on the doors of permanent dwellings. Therefore, we would not add a Mezuzzah to the entrance of a Sukkah, which is only used for one week during the year. Synagogues have inherent holiness, so no Mezuzzot are needed on their doors, though they are permitted. Traditional Jewish law requires that the Mezuzzot must be inspected at least once every seven years.
Some authorities require it even more often then that.
They have to make sure that the text is still intact and has not eroded, thus making it unfit for use. Jews have sometimes looked upon the Mezuzzah as a magical symbol. They consider it almost like a ceremonial police force, to protect them from outside harm. A few years ago, Israeli school children, riding in a bus, were killed in a horrible accident. The Chief Rabbi of the town in which they lived declared that the accident happened because many of the Mezuzzot in that town were not Kosher.