In the Teachings of the Buddha, throughout the ages, meditators keep up the practice of the Four Guardian Meditations to protect themselves from internal and external dangers. Nowadays meditators keep up this tradition.
The Four Guardian Meditations are:
(1) Reflection on the attributes of the Buddha (Buddhanussati),
(2) Radiation of Loving-kindness (Metta Kammathana),
(3) Contemplation on the loathsomeness of a corpse (Asubha Kammathana), and
(4) Reflection on the nature of death (Marananussati).
Those who practice the four types of meditation mentioned above will be protected from grief (soka), lamentation (parideva), etc, in this life, and will be also free from miseries such as be falling into woeful abodes in future existences. So, these meditations are called Four Guardian Meditations.
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