"the possibility of them inserting a sheet just where you don't
want them to should be catered for"

solution it is; despite that at first codenames are
similar to the sheet's tab  names, a sheet keeps its codename unless
programmatically changed (with the likes of:
Workbooks("test2.xls").VBProject.VBComponents("Sheet1").Name =
"AnotherName"
) or changed manually in the VBE using the sheet's properties window.
It'll keep its codename through other sheet insertions and other sheet
deletions. Not to be confused also with a sheet's index number
(Sheets(1), Sheets(3) etc. which happily changes!)