First lesson taught in law school: You can always sue. The real question is can you win, and if you win can you collect? Personally, I am more concerned about seeking a cache that has been placed in a bad location (e.g. clearly on private property w/o permission) than I am about my cache placement. I think being clear about potential dangers in the description is helpful, but I don't think that any warning or disclaimer will insulate you from liability. You just have to ask whether the potential liability is too great to continue geocaching. I think I risk much greater liability driving across town than I do geocaching.
That said,
DISCLAIMER:
I am not a lawyer, nor do I play one on the internet. I am not licensed to give legal advice. I merely offer my lay opinion and my own considerations regarding geocaching.