Attach the included test light to the receiver collar according to the manufacturer's instructions. Hold the collar by the strap with the test light attached.
Turn the boundary control knob on the invisible fence control box to the middle setting.
Walk toward the buried line, holding the receiver collar at the height of your pet's neck. Move closer to the line, listening for the audible warning and watching for the test light to flash. Note the distance from the line when the audible tone occurs and when the test light flashes.
Turn the boundary control knob clockwise to increase the width of the boundary or counterclockwise to decrease the width. Test the width of the boundary with the receiver collar after each adjustment.
Remove the test light from the collar when the desired boundary width is achieved.