The Office of Public Works has said a security company will carry out a patrol of Loughcrew in Co Meath every evening, in light of recent vandalism at the historic site.
Earlier this week, it emerged that graffiti had been scratched into a stone at the Neolithic burial monument and an investigation was launched.
The OPW and the National Monuments Service said it is latest in a series of acts of vandalism at the national monument site.