I live in an area with very dense deciduous tree cover and have little problem with my 500 and 705. I sometimes use the 500 mtbing in the woods and except for decreased positional accuracy haven't had an issue.
If you're having trouble getting and initial lock it may be helpful to reset the device as follows. Save or upload any data on the device and make a note of your setting as you'll have to redo them after the reset.
Master reset: All settings, activities, and satellite data may be erased
- Power device off
- Press and hold Page/Menu, Start/Stop and Power simultaneously
- Release buttons when the word "Garmin" disappears
After the Edge 500 is reset, it will walk through the initial setup. After completing this, leave the device outside with a clear view of the sky for approximately 15 minutes to acquire satellite data.