How Do You Secure database.yml?

The way I have tackled this is to put the database password in a file with read permissions only for the user I run my application as. Then, in database.yml I use ERB to read the file:

production:
  adapter: mysql
  database: my_db
  username: db_user
  password: <%= begin IO.read("/home/my_deploy_user/.db") rescue "" end %>

Works a treat.