Resource & Element Versioning Extra for MODX Revolution (supports 2.2 and up). Extends the core in a future-proof manner to keep copies of every change to resources, templates, template variables, chunks, snippets and plugins.
Results in the following popup message for users saving resources without the permission:
Code: 200 OK {"success":false,"message":"Permission denied!","total":0,"data":[],"object":[]}
Especially on the resource tabs, but also in the CMP.