How safe is to associate a history file with a patient record in a dfb ?

Memo or child table or memo field
( text fields in the same record seems safe but limited)

However if I am considering write the history of the patient in a child table

Is there great chances of corruption and history exchange among clientes ?

This is the first time that I came across with such a critical software

I would like to here for your experiences and ways to create tables to
such critical software

Moises