Excel VBA: Activate / Deactivate "Read-Only" on a Worksheet

Hi Experts!

Quick hopefully simple question ...  How do you turn on the "Read Only" feature in a workbook.

My Goal:
I have a data entry workbook that when the end user closes the userform (frmTracker) or when the userform deactivates I would like for the "Read-Only" feature to turn on on the "data" worksheet to prevent any modifications.  But as long as the userform (frmTracker) is "Activated" I would like for the "Read-Only" to turn Off.

Is this possible without running into Run-time Errors?  also I'm working with list objects (tables).  

Below is the code for when the userform Initializes:

Private Sub UserForm_Initialize()
    Set oSht = ThisWorkbook.Sheets("data")
    With Me
        .Width = 245
        .comboMgr.List = oSht.Range("mgrList").Value
        .comboSup.List = oSht.Range("supList").Value
        .comboSpecialist.List = oSht.Range("repList").Value
        .comboBehavior.List = oSht.Range("segmentList").Value
        ' shows today's date
        .txtDate.Value = Format(Date, "short date")
        'used a label to prevent any one changing entry
        .lblCoach.Caption = "Hi,  " & CurUser
    End With
    Set oSht = ThisWorkbook.Sheets("Data")
    Set oLo = oSht.ListObjects("CFSData")
    Me.EnableEvents = True
End Sub

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Thank you