WorldGuard safezones and flags
The glass block barrier is only available on the premium version while pushback is present in both free and premium.
Setting up a safezone is very simple: A region needs to have the WorldGuard pvp flag set to DENY
Which should already be the case for all your safezones.
When a player tries to cross into that region they will get pushed or face a block barrier.
There is support for other region plugins, such as claim plugins (Griefprevention, etc), with the premium version supporting more plugins than the free one.
Developers will be able to register their own region plugins so they can be recognized as safezones soon.
In the meantime, they can also submit pull requests adding support for their plugin.
Let me know if you're a dev and have questions about this.
Currently there is only one flag: pvp-protection. When set to deny it will remove a player's protection once they enter.
There are plans to add more custom flags, open to suggestions