SQL Security :: How To Restrict Data File Access

We have a situation where we need to restrict access to a sql server data file. That is, to prevent users viewing any tables, stored procedures, etc, in sql server or another tool. We are providing a our database as part of an application install to a customer's site which will run isolated on the customers network. However the application will have sql server logins and the system must still be able to execute stored procedures.

The setup unfortunately cannot be changed and we are trying to think of best implementations for this. Our customers are also working with competitors so we are very conscious about exposing our data structures to anyone outside of our company, hence trying to restrict access. If deployed to a sql instance on the customer site then they will have database administrator accounts on the server.