simple problem with drop down list. need solution

I have created a list named "test" which I have used as the drop down list for a column named Title in my excel. The drop down values are Mr., Mrs.

The problem with Excel is that if the user copy-pastes data onto this cell, Excel does not throw error rather it accepts that value.

I want to know how it's possible through VBA or excel features to avoid copy-pasting of non-list values on to the cells which have drop down list.

Note: I am looking for a solution where you the list values (Mr., Mrs. here) are not hardcoded into the code. Reson being I want a generic solution which I can use for other lists, and in case there are changes to the list value I do not want to go to VBA editor and change the code.

Thanks!