Laurie Miller is a reputable Arizona attorney who regularly represents women in divorce and child custody disputes. She has been having trouble collecting her fees, and her clients sometimes balk when fees mount because custody of a child is unexpectedly and vigorously contested. She is considering adopting a policy of having her clients pay a nonrefundable, earned-upon-receipt "retainer" of $5,000, which Laurie would keep regardless of how much time she had to spend on a case but which would merely be credited as the initial payment in cases in which her services wind up costing more than this amount. Under the Arizona Rules of Professional Conduct, is this arrangement permissible? If so, why (or if not, why)? In which bank account should the $5,000 retainer be deposited and why?