Put your resume up on the job boards, keep it regularly updated and let them come to you instead of you coming to them. If your employer objects - and it shouldn't because it's none of its business, tell your employer that you've always done it as part of due diligence to make sure that your skills are relevant, that you want to find what new skills to acquire and that much as you like your employer, your employer can't guarantee you lifetime employment.
As for making sure that you don't inadvertently run into your employer when you initiate contact. the best thing is to get your hands on their actual job ads, so that you can recognize them from a mile away from the way they're written.
Recruiters, at least on Craigslist, tend to use an impersonal form such as "a firm is looking for..." and a few use "our client is looking for...". Hitting a recruiter is pretty safe because they understand that part of their success derives from confidentiality. In fact, you should consider working through recruiters precisely because of that guarantee of confidentiality.
If you are doing your own leg work, the safest thing is, of course, to contact only those who have identified themselves or to directly check the websites of those companies you are interested in.
Recruiters have contacted me on Linkedin and at least in my case, Linkedin itself does a pretty good job of forwarding to me who interested in filling what positions. The catch, of course, is that you gotta keep your Linkedin profile up to date.
