Stone met Tommy Herron, commander of the Ulster Defence Association's East Belfast Brigade, when Herron moved into the Braniel estate in 1972. According to Stone, Herron took him and three friends to the neighbouring Castlereagh Hills one day and brought a German shepherd dog with them. After the four had played with the dog for around half-an-hour, Herron produced a gun and told them to kill the dog. After his three friends refused, Stone shot the animal and was praised by Herron for being ruthless. He was sworn in as a member of the UDA at a ceremony the following week. Stone was trained in weapon use by Herron himself for several months. According to Stone, at one point in the training Herron shot him with a blank round from a shotgun.