Giving a file attributes when it isn't there

Hello,
We are using a database written in FoxPro running on NT SP4 with 50+ users. This database creates an .in file whenever a user enters the database and when they leave the system removes the .in file. This is how the system knows how many users are logged into the database. We only have 20 licenses and additional license purchases are very expensive. My problem is that users will delete other user's .in file so that they can access the DB. I tried setting the rights to RWX and not delete but the DB needs to have this active so that it can remove the .in file. Any suggestions on how I can prevent the user's from deleting this file. Can i map this drive and make it hidden? If so, how and what are the ramifications of this? Thanks for the help.

You could set the maximum users of the share to the database to 20 and only connect to the share if a user starts the application. So if user 21 starts the application he gets no connection to the share. You can do this on the server with the command net share sharename /users:20

Thank you very much, I will give that a try. Take care and have a great day