You should really look at the exemptions of any policy you're considering holding. There may be many opportunities for the insurance company to sever coverage even after an accident.
Great discussion guys. I got pulled in because, while I'm not a dive instructor, I teach motorcycle classes from the basic learn to ride (MSF Basic Rider Course) to the advanced race licensing class. Most motorcyclists experience a variation of the "donorcycle*", "You's gonna die", "What are you? crazy?!?!?" on a regular occasion. Teaching people to ride is even more interesting since motorcycling has some confusion concepts such as countersteering (steer to the left to make the motorcycle go to the right). As you can imagine, motorcycling isn't without risk and once a student throws a leg over there's only so much an instructor can do to assist if things start to go wrong.
I have a story for every grey hair on my head to include wheelies, stoppies, crashes, heat exhausting and one student launching a motorcycle with both wheels more than 6 feet into the air. According to the site, the state, and my peers I have one of the best safety records, I just average 500 students a year.
I was certified by NAUI in college through a semester of 3 hour once a week sessions. I'm obviously not an expert in diving instruction, but in Motorcycle training the number of variables between students, equipment and sites means there's noticeable difference in every class. There are a lot of things that can go wrong that end up being a he said she said if it goes to court. Lawyers are great at making uncertainties seem like blame and you're not going to have each tank certified by an independent third party for air quality, rental equipment receive a certification of function for each use, etc. There is lots of place to assign liability even with the reasonable person standard.
When I first started teaching I was told that the site provided insurance coverage in the case something went wrong. I was a spry 19 years of age at the time so I took it for granted. However, after thinking about what could go wrong I got my hands on the policy (always insist on being a named insured) at 22. The provisions scared me into speaking to a contracts attorney. Per the policy, not only could the insurance company sever coverage for the company, they also had an easier option of leaving the instructor out in the wind.
I worked with an insurance broker for awhile until we found a professional instructor's liability policy that provided me with $2 million of coverage with reasonable terms for $400 a year. That also includes my work running Emergency Vehicle Operators Courses and kayaking clinics. I am the only named insured and I maintain copies of notes on every class, curriculum change dates and performance evaluations. It may seem extreme, but one instructor in Va was sued by a family for "not providing adequate training" for the head of household that took the class more than 4 years prior to his death.
It's definitely worth looking into an individual professional liability policy for any high risk instruction that you do. Unfortunately you have to balance the fun part (teaching) with work (protecting the wife's source of income).
*Based on Va statistics "donorcycle" is factually inaccurate. On Average approximately 55% of motorcycle fatalities involved drug and alcohol use over the last 5 years in Va preventing organ donation. The vast majority of the rest have too much internal injuries to donate an organ.... which further makes my point on motorcycles being dangerous.