When you say "form" do you MEAN "form" as in Userform
or do you have a worksheet that resembles a form?

if you're using a Userform,
use a TextBox for the entry.
In the Properties panel of the textbox, there is a Password Character property.
Put a "*" there.
You can create a Workbook_BeforeClose event,
or a Worksheet_Deactivate event, or both
that could be used to re-protect the sheet.
You might want to include it instead in a Workbook_BeforeSave event
so that the user cannot save it in an unprotected state.
Of course, if you're using a worksheet template instead of a UserForm,
we'll have to look closer at the change events.