Protect LocalDB from user access

I'm looking at using SQL LocalDB as the client side database which will replace the current SQL CE 3.5 database inside an in-house application developed in .net 4.

I've come across a problem that I'm not sure how to get around and that's with security setup of the LocalDB instance.

If I setup a script inside .net to create a private LocalDB instance, e.g. (localdb)\T1, then create a new database inside that instance plus add a SQL user account + password (non domain account), how do I stop the local windows users (like my own AD account) with admin level privileges from accessing the 'T1' instance + database using SSMS?

I could see a scenario playing out where we deploy the application, then we have some IT savvy user who goes snooping around and decides to install SSMS and connect to (localdb)\T1 with their windows account, which would give him/her full access to the database, which is exactly what I'm trying to stop from happening.

Some of our staff work remotely with no connection to a domain so we give them local admin rights to their pc so they can install software, so even if I could block their assigned windows login name, there would be nothing stopping them from setting up a new local admin account and logging in with that, opening SSMS then accessing the database.

Any pointers on this would be greatly appreciated!

In fact, it shouldn't be so hard. Install SQL Server on client machine using local admin account. To make you life easier, use Mixed Authentication.

After you have your instance installed, local admin account should have sysadmin server role assigned (that's normal security settings). Now, use the following:

Create new SQL Server user and assign sysadmin server role to that account. Close SSMS and log-in using new credentials. Or simply use sa account (not so good practice but in this case it's OK).
Go to "Security - Logins" and remove sysadmin role from local admin. Also, check in user mappings and take all rights "away" from local admin.

As a test, try to log-in as local admin, I guess you won't be able to log-in into server because there is no "home" database for that user. But even if you can log-in, it has only "public" role.

It's up to you to install your database and secure it - assign permission to user of your choice.

Regarding you fear that local admin can install MSSQL again: he/she can install it, but it would be another instance. That instance knows nothing about users in your instance so you should be safe.

You can also consider usage of application roles in SQL server.