Hi Kamil,
I've taken the hang problem into consideration.
In my idea, if the computer hangs, the locked record will allow edit again in 3 ways:
1) allow the same user to re-login to edit the locked record
again regarding the locking flag.
2) allow any other user to edit the locked record if it
has been locked for over a period, such as over 3 hours.
3) add function to unlock the record manually.
to do above function, I need three more fields to record
the locking status: locked, locked_by, locked_at

Do you have any other comment?