If you are looking for a unique identifier, a field that can declare a record in a database unique, you can try using a GUID.
Globally Unique ID - GUID
GUIDs are 36 characters long (32 numbers 4 dashes I think), and can be stored in nvarchar fields or in Unique Identifier fields in the database. If you are using SQL Server you can create a field, and set it to UniqueIdentifier, then in the properties set "isRowGuid" to True and it will automatically generate a GUID for that row when a record is added.
You can generate GUIDs with Vb.Net as well:
Dim MyGuid As String = Guid.NewGuid.ToString()
'OR
Dim MySecondGuid As Guid = Guid.NewGuid()
hope this helps,
Sean C