Hi, We sell hair products; both synthetic and human hair. Sometimes the customer will cut the hair and then say the hair was too short and request a refund, discount or exchange. We are searching for a safe chemical that we can apply to the ends of the hair so we know if the customer has cut it or washed it out. We're thinking about something that is only visible under an ultravilot light, but we are open to other options as well. Any ideas would be greatly appreciated.