Creating, Using & Updating A Unique Sequence In Shared Template, In VBA

I am creating an excel worksheet. Every time a user opens the worksheet (from a template), I want to get the next numeric sequence number as a reference, showing it in the sheet. The template is available to multiple users but the sequence number should be unique, ie if user Tom has sequence 1, Jerry will get 2, then Anne will get 3 and Tom's next one will be 4. I considered an ASCII text file with a number in, eg 1. Upon opening get OPEN text file, READ text file, Convert to numeric.. add 1.. use this. Convert to string.. WRITE text file. It seems clumsy and since I can only open with READ or WRITE (append no good, since I want only 1 value held), the READ allows multiple users to access simulataneously, and potentially get the same sequence.

Is it possinle to:
LOCK file
OPEN file for read
READ file
CLOSE file
OPEN file for write
WRITE file
CLOSE file
UNCLOCK file

There are likely to be several users accessing the template and the chance of them opening it at the same time is limited, but possible.