The 3 Nails.

Namo Samantabhadra.

1. The nail of perfect determination.
2. The nail of great confidence.
3. The nail of remaining with the result.

Persevere in your meditation, through it will come a pure and perfect experience free from all doubt.  Recognize the view, meditation and realization all have the same nature.  When you are free of all doubt, you will realize there is no nail to drive and nothing to drive into.  Awareness is groundless, completely transparent.

If you meditate, everything becomes a reflection of awareness.  If not, your experience will be bound by concepts and elaboration.

Remaining with the result is the union of transparent awareness and unobstructed wisdom.

This upadesha of the Three Nails was given by Younge Khachab Rinpoche in February 2010. 

Four foundations of Dzogchen meditation.

The Dzogchen kama, or oral lineage, taught four foundations prior to the practice of trekchod and thogal.

1. Immovable.
2. Unification.
3. Equanimity.
4. Spontaneous presence.

By mastering these four foundations one arrives at naked awareness beyond mind.  As your experience of the nature of mind becomes more and more subtle, you elicit the unobstructed, transparent nature of rigpa.  That subtle experience of baseless clarity transitions one to the practice of the four methods of resting which are the main practice of trekchod.