Prohibition of assignment: custodians cannot delegate functions, but may contract non-custodians for physical safekeeping under conditions. Custodians may not assign or delegate custodian functions to non-custodians, except that a custodian may retain a non-custodian solely for physical safekeeping of goods, gold or silver for clients (including mutual fund ETF schemes), provided the custodian remains fully responsible for safekeeping and associated risks, records are kept at or made available at the custodian's premises if required, and the custodian continues all duties to clients other than physical safekeeping.