Protect already placed blocks?

So my friends and I started building on a map, but now we decided to open it up to the rest of our clan. We'd like to protect it from any griefing.

I'm super new to Bukkit/Plugins etc, as we just ran vanilla on our server so today is my first day learning about it. So I downloaded Watchblock.

How do I go protect all the blocks we already placed?

 

I suggest getting WorldGuard and WorldEdit. These two plugins combined are great for protecting any stuff you don't want anyone to grief.

WorldGuard, with WorldEdit, allows you to set cuboid / square regions, which can be configured using 'flags' to include tags such as no mob spawning (mob-spawning deny) or pvp on or off (pvp allow/deny). You can find all of the help you need to use the plugin on the pages I linked or you can do '//help' in-game (once the plugins are installed).

If you need any additional help using the plugins, just shoot me a private message on here and I'll be glad to help you.