How do I release sql express database?

Questions
I have a simple app that
uses an SQL Express 2005 database. When the user closes the app, I want
to give the option to back up the database by making a copy in another
directory. However, when I try to do it, I get "The process cannot
access the file '...\Pricing.MDF' because it is being used by another
process." I closed the connection, disposed the connection, set it to
nothing, and GC.Collect(), but it makes no difference. My connection
string is "Data
Source=.\SQLEXPRESS2005;AttachDbFilename=|DataDirectory|\Pricing.mdf;Integrated
Security=True; User Instance=True" and I just keep using the same
connection throughout. I didn't see where I could detach the database
to counter the attach in the connection string.
1 - How do I RELEASE the thing? 2 - Is there a better way than just
copying the database? The app is for my husband only, so I will be able
to handle it if he actually does need to restore from backup.
Thanks!
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Answer
You don't want to copy the mdf directly because SQL keeps most of
the changes in the transaction log, take a look at the modified time
after running some queries, it doesn't write directly to the file. I
noticed this while setting up an rsync job.
Having SQL generate the backup is much safer and more desirable,
single-user or multi-user. You can provide a link to a function calling
the T-SQL which you can completely automate as far as source db and
destination folder:
BACKUP DATABASE [mydatabasename]
TO DISK = N'C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Backup\Scheduled Task Backups\mydatabasename-backup' WITH NOFORMAT, NOINIT, NAME = N'mydatabasename-Full Data
SQL 2005 had introduced another T-SQL syntax to do this, for the life
of me I can't find it. But there are ways to do it through M$$SQL
without having the full blown database server.