Choosing the right remote SQL database connection method

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VB

SQL

SQL-Server-2008R2

I have a Windows POS application with remote SQL database.
What is the best way to connect my application to database ?

I'm thinking of connecting with one of these methods

- port foreword ( currently using this methods. but it fails to connect sometimes, then I have to restart SQL server to get it connected again or wait for long )
- VPN access (but i don't want VPN user to access any data on server other than just connecting to SQL Database)
- Install local SQL server and use replication to main server ( but I cannot lock database from unauthorized access as SQL local server and POS application running on the same system )
- Remote Desktop (i don't know if this will be fast to connect to a virtual machine installed with pos Application, sale can be interrupted if network connection is lost/slow )


Please suggest me an option or if there any better option

* also let me know if i can have a local Database (should be locked like if anyone copy these files to another pc, they shouldn't be able to access any files) the pos machine itself and it will upload data to main remote server every hour.

Any help would be highly appreciated

What I have tried:

i am using port forward to connect to remote sql database, but sometimes it fails to connect to server remotely).

I would like the POS application to be faster, so i prefer local database and sync with server. same time i want my database to be protected and secure.