Although I think being completely pest free is next to impossible...I found the first of these articles on the Reefs Magazine website a while back, and figured they'd be worth sharing.
http://www.reefsmagazine.com/forum/reefs-magazine/130103-pest-free-reefkeeping.html
http://www.reefsmagazine.com/forum/reefs-magazine/139238-pest-free-reefkeeping-ii.html
http://www.reefsmagazine.com/forum/reefs-magazine/145120-pest-free-reefkeeping-iii-flatworms.html
...and just in case these links are ever moved/deleted...full text/photos below:
http://www.reefsmagazine.com/forum/reefs-magazine/130103-pest-free-reefkeeping.html
http://www.reefsmagazine.com/forum/reefs-magazine/139238-pest-free-reefkeeping-ii.html
http://www.reefsmagazine.com/forum/reefs-magazine/145120-pest-free-reefkeeping-iii-flatworms.html
...and just in case these links are ever moved/deleted...full text/photos below: