@Kace ******
you can't enter Thailand by visa-exempt repeated times any more, at some point your entry will be refused. You can join scuba diving courses, but they do not earn you an ED visa. They are just commercial enterprises you pay for joining their courses, and Scuba Diving courses are not acknowledged by Immigration offices to warrant a Non-Imm-ED visa. Maybe Scuba diving in Cambodia is better for you, if the many Chinese tourists and chinese owned businesses in Cambodia are not offending you. China practically owns Cambodia