permissions question regarding commands

I am fairly new to Bukkit, it's been working great for me so far. Basically i've been running a small server just for my friends, and I wanted to be able to invite guests to view my world but i've been reluctant because of griefing potential. I already have permissions configured to make admins invulnerable and able to build, and anyone else not able to do either, but what about slash commands? Is there a way to deny these specifically? I just want to make sure that there's no way that guest players can do things like unbind my portals and stuff. Also, is there a way to make sure players have to be authenticated with a real account to come in? I figure this would help reduce the likelyhood of shady characters potentially finding the server and coming in (i have both daily backups and shadow copies every two hours, but still). Nothing is really preventing someone from finding my server randomly or by port scanning and coming in.

Any help and/or suggestions would be appreciated.

OS: Windows Server 2008 R2 X64
Java: J6 U22 x64
Bukkit version: 766
Java run command: "%ProgramFiles%\Java\jre6\bin\java.exe" -Xincgc -Xmx1G -jar craftbukkit-0.0.1-SNAPSHOT.jar

Plugins (so far):
SQLite
Persistence
Wandmin
Permissions
Travelportals
Zeus
SimpleGodMode

All plugins are working properly as far as I can tell. My server permisisons are set through the Permissions plugin.

 

As long as the server is set to online mode, you won't have to worry about people who don't own a real copy of the game. Not that a good portion of the griefers out there don't own an actual copy though.

As for the default commands, you can use DefaultPermissions for those or just rely on the ops.txt file. You should also look at BigBrother or something like that for that just in case moments. Another way to prevent some griefing is to use something like Towny to set up a city and only grant building access to a limited area for each person.