Basically, what it would do is, when a player uses xray, it teleports them right into a jail. Here is how it would work. 1: Player uses xray. 2: He see's red wool or some type of alarming block. 3: The block triggers the teleportation and sends him to jail. I could do it but I am rather busy on another plugin. If anyone wants to make it, please feel free.
Minecraft doesn't work like that. The server is not able to identify whether a client can see a block or not, it simply sends out chunks to the clients. This is also similar to the way in which it is impossible for an unmodded build of CraftBukkit to add extra blocks or items to game without a client mod.
I know! His custom block system without any mods is just unbelievable (quite literally ). I'm still waiting on the source...
This is absolutely possible, TrustCraft is a pro developer. He will make it himself, and make a troll-thread about it i guess =) Lol -.-
Well, there's Honeypot, but that bans them. Haven't used it, maybe there's an option as to what command it executes when the block is broken?