It really depends on the timeframe you utilize to define trend.
If you are long term trend follower, you'd likely trade the weekly chart and use the monthly and daily to pinpoint your entry and exit.
In trend following exit prices are defined relative to trend rather than to a forecast or anticipated target. Many participants in the late 70's sold at 350, 400, 450, 500, 550, 600 etc because of strong belief that price was "too high".
Price had other plans and subsequently peaked at 850. Many trend followers started selling in volume right after that.
I assume you want to know where to exit a profitable trade in the current day.
Assuming a long-term trend following approach, any
closing price on a
weekly basis lower than the 50-week moving average is considered cause for concern by many long term trend followers.
How much to sell at that point is a function of your system and associated discipline in actual execution.
The current gold situation has the look and feel of a strong long term uptrend.
35 year gold chart
http://www.gold-eagle.com/charts/35yeargold.html