MS SQL datetime precision problem

I know you said you can't change the type, but if this is only to maintain compatibility & your using 2008 you could change the lastSaved field to DATETIME2 (which is fully compatible with DATETIME) and use SYSDATETIME() both of which have much greater precision.

You could add an integer revision field to your order table. Every time a user saves the order you increase the revision by one. Then its easy to check if somebody has altered the order or if the user who wants to save the order are on the latest revision.