I have the following problem to my database, please help me

1. I have a database/form my problem is that every time users open database they accidentally delete the existing records of a customers I tried to lock field and when I add new records is locked, how to lock out editing a field on a form after update or first entry
2. I have an Identity document of a customer with 13 digit as follows: first 6 digit stand for date of birth like 550101 this person born 1955.01.01 and second 4 digit stand for gender registration e.g. if Male digit stand between 5-9 like 5309 and if is Female digit will start between 0-4 like 0309 and the last 3 digit is the country code
How to do input mask or Validation rule to able to identify Identity document of a customer as to avoid writing wrong date of birth and registering wrong gender
The First 6 digit represent Date of birth
The Second 4 digit represent Gender
The Third 3 digit represent country code

Please assist
From Piet

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Reply from Richard Rost:

1. Set ALLOW DELETIONS to False and give them their own data entry form.

2. I would set up separate fields for each of these (a DOB field, a gender field, etc.) and then use STRING CONCATENATION to assemble your custom value as a CALCULATED QUERY STRING.