Currently we use a spreadsheet that is accessed by multiple users. The Accounting department is the only department that has the password to unlock the spreadsheet to edit locked cells. However, we have encountered an issue. While accounting is in the spreadsheet, another user can open the spreadsheet and it does not open as read-only. In the past, if someone was already working in the spreadsheet, any new user would be notified as the spreadsheet opening as read-only. This isn't happening anymore and I am not sure how to secure this. We do not want multiple users being able to edit a spreadsheet when someone is already in the spreadsheet editing. What can I do to fix this issue?