Gardaí are investigating an attack by vandals on historic Lissadell House, the ancestral home of Countess Markievicz which is at the centre of a right-of-way row.
Entrance gates and other barriers on the estate were damaged and removed. Slogans were sprayed claiming there has been public access to the 162 hectare (400-acre) property for more than 100 years.
The damage was discovered by owner Eddie Walsh and his 12-year-old son, Harry, at 7am yesterday. A heavy wrought-iron gate was cut from its hinges, carried 20 yards and dumped in nearby woodland.
The vandals are believed to have used an angle-grinder and chainsaw just hours before hundreds of visitors were due to arrive for an open day on the estate. Damage is estimated at €5,000.
Gardaí, including a forensics officer, were on the scene soon after the alert.
Mr Walsh said: "The attack seems to have been well planned. There is little doubt it was deliberately aimed to disrupt the open day." His wife Constance Cassidy said: "We feel it's a thing that was planned for some time. It's very unpleasant."
An 18-month-old dispute escalated earlier this year when the owners closed off vehicle access to a nearby beach through part of the estate. Locals claimed they were being deprived of a right they had enjoyed for more than 100 years.
The owners said they had established there was no such right and they were not shutting down access, just controlling it for security and safety reasons.
Mr Walsh threatened at the time to walk away from the estate or develop it as a holiday village instead of maintaining it as a historical monument. A spokesperson for Lissadell Action Group said: "There is no way we would condone the vandalism."