When it comes to sites like Eagles Nest, I think it would be great if all the major training organizations could agree to make a statement like the NSS-CDS:
Statement from the NSS-CDS Training Committee on Eagles' Nest - NSS CDS
They came out and said straight up - there is no cavern area at Eagles Nest, and people shouldn't be doing any courses there unless the student is fully cave trained. There is no gray area there. And if the other training organizations had the same type of statement, then taking OW and cavern students there is a clear standards violation, and now there is the ability to enforce some penalties for people paving the way for the normalization of deviance that gets people thinking that Eagles Nest is somehow "safe" in the entrance room.
Unfortunately, there are shops that use EN as a training area, even for open water divers. If their training organization doesn't specifically forbid this, then it may be frowned upon, but it's not a clear standards violation, and nobody is going to do anything.
I think the first step would be to approach and petition all the major training organizations to agree with a statement like the NSS-CDS published. The next step would be to post a sign that states the statement, and advises students to report to their training organization if an instructor takes them there. (Someone posted an example sign earlier in this thread - I think that would be awesome)
Now you have a clear standards violation to shops taking students there that aren't ready - at least at the most basic of certification. It also makes it easier for students to know that their instructors are violating standards, and makes it much easier for these incidents to be reported.
Does this keep everyone from going there? No...but I do think that having a site like EN being used for training of non cave divers does make it SEEM like a safe place - particularly to students who have been there, who will likely feel safe going back and diving there on their own. As it turns out, the most recent incident at EN is a great example of this. The guy had done training there, so why would he think it wasn't safe to go back and dive it once he had more experience than he did in class?
I think limiting divers exposure to the area by limiting the number of people learning to dive there is a great 1st step in decreasing incidents at this site.
The fact that EN lies in an area that has easy and cheap access to the public is the problem, because the diving public sees that area as a resource for training. There are other deep and complex cave systems in Florida, but access isn't as easy, so we don't see similar types of incidents there.
Beyond limiting access to training, I think that further limiting access to the site could be done rather cheaply. I think a gate across the access road (no lock - just a gate that has to be physically opened to pass) with a sign on it saying that non certified cave divers found beyond that point with dive gear are trespassing, and are subject to fines and arrest. I don't know if law allows it, but confiscation of dive gear used in commission of the trespass would also be a nice touch and good deterrent. It's certainly doable for people who are violating limits for fishing and such...And just ask the ranger to periodically drive past the area. If they catch a vehicle there and there's no cert card on the dash, and it's clear someone is diving - boot the vehicle. Done and done. It's not like anyone knows how often or when the ranger comes by, so I imagine most folks would be a little nervous about a sneak dive like that.
Obviously there are ways around the stuff mentioned above, and I firmly believe that once you make something idiot proof, the world finds a way to provide a "better" idiot. That said, I think these measures would go a long way towards a "good faith" effort to prevent the deaths of uncertified and undercertified individuals at places like EN.