Question Author
Thanks to all of you who took the time to reply to me. The question certainly awoke a difference of opinion. I've settled on 'dob in' as most of you have chosen this as your answer, although I have to say I believe that 'dob on' is more gramatically correct. You don't tell or report 'in' an individual or something, surely telling or reporting 'on' an individual or something makes more sense. Thanks again, everyone.