I worked as a designer on retainer for 14 years. I got a monthly check and worked unsupervised at home – except for a once-a-week, face-to-face, hour-long meeting. Meeting the goals and deadlines was the measurement, not the number of hours worked. This probably means I worked pretty hard for them!
Every year we’d plan what was needed for the next year. I’d prepare a bid and we’d divide it by 12. Of course, other needs would pop up and we’d call that “extra work” and it’d be billed separately. This way I was not considered an employee but a subcontractor. They felt more comfortable providing their own annual contract than one I wrote – and that was fine with me. The work was an addendum to the agreement each year.