Macro into locked cells

im making a sheet where employees, after making a phonecall, hit a macro button to date/time stamp a cell. The problem being that we want these cells locked so after using the timestamp macro the employees cannot go in and alter the times.

the current macro is very simple-
//
Sub NOWTIME()
ActiveCell.Value = Format(Now(), "MM.dd h:mm AM/PM")
End Sub
//

If anyone could help it would be greatly appreciated.

currently the cells are locked and i have already passworded them

You can protect and unprotect the sheet in VBA with

ActiveSheet.Protect Password:="myPassword"
ActiveSheet.Unprotect Password:="myPassword"

You should then probably put a password on the VBA code to stop them looking at the password

the one problem that i have run into is that now they still have the ability to over-write the protected cells by just re-runnign the macro.. is there any way for the macro to only write to the cell if its empty?

current macro code:

Sub NOWTIME()
ActiveSheet.Unprotect Password:="pw"
ActiveCell.Value = Format(Now(), "MM.dd h:mm AM/PM")
ActiveSheet.Protect Password:="pw"
End Sub

sure, just put a test at the start of the macro

Sub NOWTIME()
if activecell.value= "" then
ActiveSheet.Unprotect Password:="pw"
ActiveCell.Value = Format(Now(), "MM.dd h:mm AM/PM")
ActiveSheet.Protect Password:="pw"
end if
End Sub