Yes get it in writing. I have it in my contract too.
But I don’t publish a client list on my site - several reasons.
Not having a client list has made no difference to the amount/quality of work I get.
I don’t think clients want to see themselves lumped into a big list of other brands. When you’re freelance you have to make your client feel as if they are #1 , they don’t want to know about anyone else. I think that’s why they don’t like it. They don’t want to be collected like some kind of ‘badge.’
I can think of examples where designers have lost out on work because there was a brand that saw a brand on their client list that they didn’t like.
Because I don’t have a list published on my site I can then use my own discretion when talking with other clients about who I’m working for/have worked with, I don’t want to tell everyone everything about my work.