I am not sure about your “shared” statement, one of the best uses of dropdowns (in my humble opinion) is that they are perfect for shared work book as you limit the damage done by the wrong type of data input, I have used this many times with dependant drop down validation. I put all my drop down lists on their own sheet and hide the sheet, works for me as most users do not try looking for hidden (most would not know where to start ) if you need more protection protect the sheet.
Manish, not sure which version Excel you are useing but you will have to unshare the worksheet to get your tab back do your validation and reshare your worksheet