I think the fact that I tried to set up a rating system for caves and did set one up for more basic overheard environments indicates that I believe there should be some kind of an advisory system about dive difficulty. My attempts to create it showed me how unlikely it is to happen.I think this is kind of my point. Other extreme sports rely on the individual to know their limits or face the consequences whereas I think there may be a false sense of dive ability when someone holds a card saying they have been trained, even if it has been many years since their last dive.
I used to be an avid cyclist, both mountain biking and on the road. I even had some formal coaching and had my collegiate license. Trail ratings were key for some runs but even for some of the more technical trails, our club would hit green trails for warm-up. I know skiers who do the same. They don't just hit the black diamond run without warming up or being well into their ski season.
I think a hybrid model would be more beneficial to the sport and maybe even the environment. I think that those agencies that do requrie so many dives to keep their cert active are on the right track, but the question then is what happens to the vacationing diver who may only get out one or two weeks a year?
I don't really know the answer to any of this but I think this a good discussion.
The problem with requiring a certain number of dives to maintain a rating is the nightmare of policing it. How is an agency to know how many dives I have done in the past few years? Will they take my word for it? I know agencies that have such requirements, but as I indicated in an earlier post, if you want me to produce a dive log that meets certain specifications, I can have it in no time.
Many advanced certifications require a minimum number of logged dives, but that is really just a fuzzy gatekeeper that is more of a guide for the student than a real requirement, since it is so easily faked. The real requirement for the advanced certification is what you demonstrate during the course, not some meaningless dive number required to start it.
Many years ago I was on a dive boat setting out for dives in Cozumel, and our group included a couple we had just met. He was well into middle age and financially well off; she was (I know it's a stereotype) his young, very beautiful, trophy wife bride. She had just been OW certified for this honeymoon trip, but he made sure everyone on the boat knew we were in good hands with him on the trip--he was a certified Rescue Diver. He showed us all his card. (I was then just AOW.) Well, she turned out to be a very good diver, far more polished than her new certification would lead you to expect. He was a wreck. On both dives, the DM literally held his hand throughout the dive. He remains one of the very worst divers I have seen in my life.