First off, let everyone know ahead of time where things will be tanked. You need at least two positions to alternate between because of the desecration.
Second, assign DPS to specific targets for focus firing but also make sure they are interrupting as well while killing the target. For example one of the several times we've done it I had myself and the tank on the Guardsman to kill and interrupt while the other two DPS handled the Officer. Kill the adds and interrupt the heals fast enough and any time you have on the boss will gradually widdle him down.
This fight is largely about exercising control. With proper technique you can basically keep things going almost indefinately (depending on mana efficiency). Focus on control in this encounter and the rest will fall into place.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.