IIRC the Turtle system is a long term trend following system that gets in and out with a breakout trigger. (Something like "buy if the close is higher than the close of the last 14 days".)
Like Gotta_trade says, long term trend following is a profitable strategy (witness Aberration's well documented success), but it has large and lengthy drawdowns.
There are many CTA's, managed futures funds, and system-following brokers that could execute a long term trend following system for you, if you like.