As Bob Ray puts it: "If you want users to see only their own pages, you need a separate User Group and a separate Resource Group for each user (name both after the user to make things easier)." You cannot just associate a user with their dedicated resource group; instead you have to give the user their own user group and then associate that user group with the resource group.
The trick to making this work in practice is to install the DefaultResourceGroup plug-in and follow Bob Ray's tutorial at
http://bobsguides.com/user-specific-pages.html
Details are in Bob Ray's tutorial, but essentially it places all new resources into a default Resource Group or groups.
Here's the twist to the trick: rather than setting DefaultResourceGroup up as Bob Ray says, I suggest you disable the plug-in, duplicate it, rename it (as ParentResourceGroup) and modify the duplicate as described by hochmohr (and approved by Bob) in the MODX forums here:
https://forums.modx.com/thread/81773/inherit-parent-resource-group---problem-with-defaultresourcegroup#dis-post-451127
That code creates a plug-in which adds new resources to
the same resource groups as their parents. (This won't need any resource group specified for the plug-in, either.) For managing users who just post to one area of the site, including in Articles, this is perfect, and quite powerful.
And yes, you'd think after all the effort the MODX team went to to make the user management powerful and super-granular, there would be more documentation of this or even some automation. Sadly, no. I have a few user management notes at:
http://shorewalker.com/site-building/modx/how-to-set-up-a-modx-site.html
The good news is that the MODX team knows user management is an issue. I am holding off documenting further because MODX 3 apparently makes big changes to user management.
