I have been working on a month-to-month retainer for several years for the same firm, and have been asked to propose changes to my arrangement that would "provide more stability and predictability", partly as an acknowledgement of my contributions (which, it is agreed, warrant much more stability and recognition than an "at will" retainer), and partly to ensure that I cannot be easily terminated (e.g. should the work I do run afoul internal politics).
What are my options in this case? I do not want (and I'm pretty sure my client does not want for me) to become an employee. Ideally I would like the changes to my existing arrangement to be minimal, or at least simple, with the primary goal of ensuring that I continue to make at least as much as I now do, doing essentially the same work, for as long as possible, without suddenly loosing my retainer fees. I assume I can ask for things like a few months' notice of termination, or a few months' fees following termination; but I'd prefer (and believe I can get) more. I've been working for my client for over a decade, and the client has recently been funded for at least another 5 years. Can I ask for a guaranteed contract for 5 years?