The issue is the way world guard works is it listens for block events in the guarded area and if they happen it stops them. Now tekkit items do not call the same events and are not monitored so when they are used to interact with the guarded region they just bypass it. The only way to fix this is have someone edit worldguard in such a way it picks up tekkit events (nuke blowing up, mining laser) or to just disabled them completely. Sorry for the horrible answer but ive gone through the same issue.
