Not all GPSrs are created alike. Some work better than others, depending on their design. I have been into Geocaching for a little less than a year now and have noticed something interesting. I have also created 20 caches of my own of various types and sizes.
My GPS is a Garmin GPS-12 Personal Navigator and one of the reasons I bought it was one statement in it's advertizing that caught my eye. It is suppose to work "...under heavy tree cover...". Apparently there are many others, such as the little yellow Etrex ones that stumble and fall under those conditions.
My point is this, if you're going to place a cache out there in the woods and there's a heavy tree canopy, use a GPS that was designed to be there, not one of those that works great on the water or the highway, since trees don't grow there. Furthormore, don't just take a quick reading, take several and then walk away from your cache several times and see if your GPS brings you back to the same spot.
I prefer to use Statute Miles(for the moment) on the Hiway and Metric on the ground and walking. You can get closer to the cache in Metric when your partner is using Statute Miles. Try yourself, it works!
If you think you are leading, but no one is following...you're just taking a walk!