In my current work, we organize a CS conference every year, and we also have a journal in the CS field. However, we are currently facing a problem with some reviewers. On few occasions, we have a couple of reviewers who rejected the sent paper, saying they have not been appointed for the current year. However, they have acted as reviewers in previous versions of our conference. The question would be if it would be sound weird to ask a reviewer if he would like to form part as a permanent reviewer of the conference or journal. Are there any suggestions about how to deal with this?