Hey Jack, You will have to dive into the security settings.
There you can determine what can and can't be seen by different users.
You could set up different privillege sets if you want where each set is only allowed to view records of a certain field.
Or you could have a global field set with the users field upon opening the file and then use that value to determine the records that this user can see. This is also in the privilege sets.
See "Editing record access privileges" in FileMaker Help and check out this particular sub section: "Entering a formula for limiting access on a record-by-record basis" for a description of how to set this up.
And another key trick here is that with this type of record by record access set up, any find that the user or a script performs will automatically omit records for which the current user is not permitted to view.
Thanks Phil & Guy.. nailed it!