Marshall has studied the Enneagram for 15 years. Marshall worked for the Enneagram Institute for nearly 4 years, where he created the technology that powered the RHETI (Riso-Hudson Enneagram Type Indicator). During that time, he attended several Enneagram Institute trainings as part of the Riso-Hudson Certification program.

Marshall is a member of the International Enneagram Association and has participated for several years in reviewing speaker proposals for the global Enneagram conference.

Marshall has been a student of the Diamond Approach in the Ridhwan School for 13 years. He has worked directly with A. H. Almaas on technology for the school.

Marshall has studied and received trainings in a wide variety of psychological, therapeutic, spiritual, philosophical, and inner work modalities.

• Many kinds of meditation
  • Vipassana (Buddhist)
  • Microcosmic Orbit (Taoist)
  • Kath / Hara (Diamond Approach)
  • Zazen / Being Meditation (Zen)
• Internal Family Systems
• Bioenergetics (Alexander Lowen)
• Somatic Experiencing
• Continuum Movement
• Inner Relationship Focusing (Eugene Gendlin)
• Self Acceptance Training (Dick Olney, Cherie McCoy)
• Various Breathwork modalities (Reichian, Holotropic, Wim Hof)
• Object Relations Theory
• Family Constellations
• Integral Theory (Ken Wilber)
• Spiral Dynamics
• Soul Without Shame (Byron Brown)