Tell them the next time they do it they're fired.

Use UI security to hide the Reverse icon from all but senior users.

Hello Shane,

I was training about two days ago and I felt I couldn't emphasize this enough. Can you please elaborate on how you use UI security to achieve this.

1. Log on as ADMIN
2. Open the screen where the restriction is required
3. From the menu, click File, Customize
4. Select an existing Profile or create a new one (a profile saves the UI customizations so they can later be applied to users)
5. Scroll through the available controls and de-select any that you want to restrict (in this example, de-select cmdReverse)
6. Click the Ok icon
7. Navigate to Administrative Services, Assign UI Profiles
8. Select required user ID and the Profile ID created in step 4

Sage really should have an option in GL options to ask if you want to allow the reversal of subledger batches.
That way if for some reason something is posted to the wrong period or account or something else, they could turn it on, reverse the batch and repost and then turn it back off.
Or at the very least a dirty great warning coming up saying "Subledger amendments should happen in the subledger, reversals here will not be reflected in the subledger".