Cal. Lab. Code § 4156

Liability for compensation does not attach to any employer of a person excluded by paragraph (8) of subdivision (a) of Section 3352 from the definition of “employee” for an injury to or the death of a person so excluded which occurs on or after the effective date of this section if the employer elected to come under the compensation provisions of this division pursuant to subdivision (a) of Section 4151 prior to the effective date of this section by purchasing or renewing a policy providing comprehensive personal liability insurance containing a provision for coverage against liability for the payment of compensation, as defined in Section 3207 of the Labor Code, to any person defined as an employee by subdivision (d) of Section 3351 of the Labor Code, however, this section does not prohibit an employer from providing compensation pursuant to the provisions of this chapter.