Let me simplify...

If the database is on the user's machine and the user has local administrator permissions, there is nothing you can do to keep that user out of the database if they want access. You can slow them down, that's all.

If you want to restrict access, the database needs to be on a server. The bear minimum of people must be admin of that server (typically sysadmins and maybe DBAs), the users then have logins to SQL and only the rights you want to give them.

TL;DR If you give the database to someone (put it on their machine), they can do what they like.