A ground rod cap is provided. The cap includes a body that fits around a ground rod, ground rod clamp and ground wire at their point of connection. The body retains a filler material within an internal cavity. In some embodiments, a portion of the body acts as a barrier to retain the filler material. In some such embodiments, the filler material is positioned within the body prior to installation of the cap on the ground rod connection components. In some embodiments, the filler material is located in an airtight cavity until installation. In some such embodiments, a shrink-wrap material is placed around the body to make the cavity airtight. In other embodiments, the filler material is retained within at least a portion of the cap by an internal barrier that breaks as the cap is installed to allow the filler material to flow around the components.