Alas, there's no way to "lock" cross-reference or index tags, per se.
But there is a way to ensure (that's with an "e", as in assure with general certainty, as opposed to insure, with an "i" or absolutely guarantee that there will be no problem) that you keep your cross-reference and index tags.
The problem stems from editing within InDesign layouts. By default, cross-reference and index entry tags are invisible when you edit copy within InDesign layouts. As an example, I've highlighted a passage from a book I laid out some time ago. All I did (I thought) was highlight the space before the acronym CPA. But actually, I also highlighted the index entry for the appearance of that acronym on page 22.
I don't know that, of course. When I highlighted it, it only moved across what felt like one "character", but it also picked up the invisible index tag. By default, it doesn't even show that I have it selected in the Index panel.
Currently there are two ways to make that invisible index tag appear:
1a. Select the Type>Show HIdden Characters menu command (Keyboard shortcut is Cmd+Option+I on your Macs; Windows users would find that shortcut as Ctrl+Alt+I). This works like MS Word's Show Invisibles option, and shows things like spaces, tabs, indents and in this case index/cross-reference entries, as shown in the illustration below.
It turns out that we not only have one index/cross-reference entry, we actually have four, as highlighted by the yellow ovals. The index entries are shown as a cyan carat character below the type baseline, and two cyan dots like a colon in the X-height of the line. You can now at least see and highlight either the space character (one cyan dot in the middle of the X-height) or the index entry, but differentiating between the two is very tight and it's still all-too-easy to accidentally edit out an index or cross-reference tag. Which is why I strongly recommend ...
1b. (Better) Edit your catalog copy in the Story Editor panel. You'll get the results you by first clicking your text tool anywhere in the block of copy you want to edit and either selecting the Edit>Edit in Story Editor menu command or using the keyboard shortcut Cmd/Ctrl+Y shortcut, depending on whether you're working on a Mac or Windows system.
As shown in the image above, highlighted with green circles, index and cross-reference entries are much easier to see -- and much easier to not select -- in the Story Editor panel. It's extra step(s), but as I said it better ensures that your creative staff doesn't accidentally delete index or cross-reference markers which would be painstaking to find and difficult to adequately replace.
2. Once you pick your option, implement and enforce a policy where a.) all systems have Edit>Show Hidden Characters on and (ideally) b.) all copy edits of the catalogs is done from the story editor and index/x-ref markers are never edited with copy. The first part is just making the setting on all your systems and the second will quickly become muscle memory and second nature. Don't forget to document this yourself so you can spread the knowledge to new users as they come into your shop.
It's not the perfect answer, but it should work for you from here on out. If this is clear and viable for you now, please mark your question as answered. This alerts moderators to archive your question and this answer so it will benefit other InDesign users who find themselves in a similar spot.
Hope this helps,
PHEW! Thanks for your detailed explanation. I already knew all that and my problem isn't that the couple people who are my employees don't know about showing invisibles and making sure they keep any tags with the text when editing/moving. My problems is that we use a few freelancers and an occasional new employee who is wet behind the ears and not familiar with the finer points of InDesign. Those are the people I worry about.
I'll have to resort to a training session every time we bring someone new in...UGH.
I agree it's not the best answer. But it works. And if your organization is explicit about it, problems can be stamped out and turned from a common and recurring problem to a rare one.
As someone who's been on both sides of the freelancer/consultant divide, I'd recommend using this as the excuse to develop a best practices document that illustrates idiosyncrasies/issues relevant to your workflow for your stringers/new hires. It's a relatively simple process which will pay handsome dividends far forward of the point of where you implement it. And save you training time by including it in new hires' orientation packet.
If I can help with this, please feel free to contact me offline. I do this for my clients all the time and it works like gangbusters.