andyexeter

Post Lockdown protects your site-critical pages and posts by disabling all non-admin users’ ability to trash or delete them. 
It can also lock pages and posts, which will disable editing of the post as well as disabling trashing/deleting.
The plugin adds a new options page under the Settings menu in your WordPress admin panel which allows you to quickly search and 
select for all pages and posts of any post type. When you find the item you want to select, simply click it to move it to the right 
box and click Save Changes.
See the screenshots for an example of what an Editor would see when they view a list of posts with some locked and protected.

Post Lockdown

Works very well, my only criticism is that private posts/pages should be lockable, ie private posts should appear in the search form.

In order to lock them currently you need to publish them, then lock/portect, and then make it private again

Update!! the developer added the minor feuature request/bug. This plugin is now perfect!

Now perfect

I think the plugin is really useful, otherwise I wouldn't have made it ;)

Great Plugin

Allows admins to protect selected posts and pages so they cannot be trashed or deleted by non-admin users.

tom.maitland

Restrict Page Parents is a lightweight plugin to enhance the user permissions features of WordPress. It changes the option to set a page parent to only show pages owned by the current user. It can also be configured to force users to select a parent page before they’re able to publish or save.
Restrict Page Parents prevents users from adding their own pages under sections of the site they do not own or are able to manage. Users can be confined to their own section of the website, making your site permissions much more secure.
Permissions can be configured for each user role, each individual user and turned on/off based on post types.
You can find out more about the plugin <a href="http://www.tommaitland.net/restrict-page-parents" rel="nofollow ugc">here</a> or on the <a href="https://github.com/tommaitland/rpp" rel="nofollow ugc">Github project page</a>.

Restrict Page Parents

Restrict Page Parents restricts page parent options to those owned by the user, with the option of forcing a page parent.

Post Lockdown vs Restrict Page Parents