Initially impressed by Manson's songwriting talent, Dennis introduced him to a few friends in the music business, including the Byrds' producer Terry Melcher, whose home at 10050 Cielo Drive would later be rented by director Roman Polanski and his wife, actress Sharon Tate.
Dennis recorded a Manson song for the Beach Boys, originally titled "Cease to Exist" but reworked as "Never Learn Not to Love" (1968), a single B-side.