He and his son Marcus considerably improved the landscape to the extent that it was described in the Parliamentary Gazetter of 1844 in the following terms: "The mansion built by Sir Walter Synnot and the demesne attached to it is laid out and planted in a tasteful style.
Their son, Brigadier-General Arthur Henry Seton Hart-Synnot inherited the demesne on his father's death in 1910 and sold portions of it to his tenants prior to 1919 under the Land Acts.
He demolished part of the house c.1918 after it had been damaged during requisitioning as military accommodation during World War I and donated the remaining avenue and glen to the National Trust in 1938.
Due to the repairs required and the huge cost of rates which were inflicted at war times, the Hart-Synnot family later demolished Ballymoyer House.
Sadly, Johnny Bell who was unmarried and lived alone in the house was murdered whilst a serving part-time member of the Ulster Defence Regiment.