You should only use a professional investigator who has full knowledge of the provincial and federal laws regarding monitoring and surveillance. In the event that you ask a friend to take photos or monitor them, they might use an illegal technique such as wiretapping or trespassing on private property which can lead to criminal prosecution. Additionally, once someone knows they are being watched, it becomes more difficult to obtain evidence in the future. Surveillance and tracking measures should only be conducted by a professionally trained and licensed PI who knows what practices are legal and admissible in court.