To split a stone use a stone chisel and small sledgehammer. Safety goggles and leather gloves are needed to be avoid injury. Marking a line with a grease pencil where you want it to break cuts fieldstone. Score along the line with sledgehammer and chisel to score along line. With chisel on line hit hard with hammer.
Flagstone is marked and scored on both sides.
Place on a 2x4 with scored line 1 in. To check the wall's slope make a gauge by nailing three 1x2 s to form a 90degree triangle. Using a stakes and string outline the wall, the trench will need to be 6 in. Bonding stones are set at each end of the trench using the heaviest stone first and then every 4-ft. between. The first layer should be as level as possible, with the flattest side of each stone up and the best side should be faced out.