The only downside to that approach is when there's a sea change in that area of the law. For instance, if the CWA all of a sudden became much more simple, the number of viable legal work in that area could take a huge drop. Of course, I don't think a complex statutory and regulatory scheme like the CWA could become "simple" overnight so you could probably see the change coming and make adjustments in your practice as necessary.
Yea, the key I think is becoming one of the foremost experts in a large but complex area of law. Because I’m environmentally focused NEPA, CWA, CAA come to mind, but I am sure there are others in other areas of law. To keep your credentials as an expert in addition to doing cases you would have to write about the subject as well and get published. If you’re doing that kind of research on the issue your likely to see some kind of sea change on the horizon, and because your already an expert in it you probably have idea on how that change in the law is going to affect the regulated people, so your still ahead of the curve even when/if the law changes and that would mean even more people would come to you for advice.
Being an expert on anything I think means life long learning and expecting the changes that come along. If that’s your only job it’s not hard to stay on top of, or even be part of, chaining the law if you’re a recognized expert. I mean that’s what our professors do, teaching is secondary (to the school) to researching and writing on the subject of their expertise. I mean if you do a search for clean water act law review articles this guys name comes up like every five, he is listed as an author of a bunch of lawyers guides to the CWA. He just keeps abreast of the legal issues, writes papers on the changes and get them published then parlays that expertise into working on cases for other firms.
I know another lawyer who just does endangered species act listing petitions. That’s all, she’s done like over 100. The pays not that great up front because its public interest, but she wants to work from home and raise her kids, so its good for her she can do everything she needs to do from her home office and be there as a stay at home mom while still keeping her legal skills and getting some $. Environmental organizations approach her with an idea to list a species, she writes up the listing petition with all the legal requirements, and arguments for listing and they add the science then she submits it. She does sliding fee depending on how much money the origination has (or how much they raised from like a “save the spotted mouse” campaign).
Where she really makes her money is if the agency does not rule on the issue in 90 days or the ruling is arbitrary or capacious you can sue, and the statute includes an attorney fee provision so every 90 days if the agency you got a new suit, and most settle out of court so you get your fees. The animals looses most of the time, but you at least get your fees (including the fee for the listing petition). Its not steady income, but comes in lumps when you get your fees.
I’ve actually written a listing petition, and its not that much work if you know the law and the arguments to make.