When a user enters a field, lock that field on that record, not the whole record.
Record locking causes issues all the time, and just isn't necessary. I don't need user x to not be able to edit a contact's email because user y is fixing a typo in the same contact's last name.
I would say this could even be optional, and instead of locking it give a warning when two users are editing the same field on the same record at the same time, and ask the second user if they want to keep modifying the record or view the update. Making field/record locking optional would also be a great feature, although I'm not sure how feasible it would be.