Term Limits for Supreme Court Justices?

John Fund certainly makes a persuasive case in the Wall Street Journal. Fund calls for 18 year limits, an exemption for currently seated judges, and one justice retiring every two years, giving each president at least two shots at the high court. In general, I don't like tinkering with the founders on issues like this, but the argument that does carry a lot of weight with me is the enfeeblement that so many justices undergo before they will let go of power. The sight of a person who is incapicitated for all intents and purposes sitting on the highest court in the land is not a pretty one. Food for thought, in any event...