Managing New Record Validation With Binding Navigators

Using Binding Navigators to tables in datasets. How are you all managing putting default values into new records? How are you handling "general" row validation before allowing them to save the record? We actually save on the current change event of the BN right now - client does not want to use a save button. But still how would you "stop" the current change from happening if the record was not yet valid enough (like filling a couple of foreign key fields)?