If you want to prevent the users opening your database from the G:\ drive, you can do a simple check with code like this in your startup form:
Dim strMsg As String
If CurrentProject.Path Like "G:*" Then
strMsg = "Please copy this database file to your " & _
"local disk and open the copy instead of this one."
MsgBox strMsg
Application.Quit
End If
If you also want to prevent them opening the database from a different drive letter mapping or a UNC path, you could add a file such as NotFromHere.txt to the folder where your database file is stored.
Dim strMsg As String
Dim strFilePath
strFilePath = CurrentProject.Path & Chr(92) & "NotFromHere.txt"
If Len(Dir(strFilePath)) > 0 Then
strMsg = "Please copy this database file to your " & _
"local disk and open the copy instead of this one."
MsgBox strMsg
Application.Quit
End If