I own a Quattro too, it is really good machine. The slower you swing the coil the better. For the really trashy area I would suggest purchasing a smaller coil. You would not believe how many coins I found with my smaller coil that I missed with the larger coil. Also I would suggest purchasing a 11 inch pro coil, it is better then the original that the Quattro came with. You can find the information about the coils here
http://www.findmall.com/read.php?19,1055627. I think the most important thing to do on the Quattro is to noise cancel. I noise cancel before I start to hunt, when moving to a new area, and when I make adjustments to the detector. I always noise cancel with the coil on the ground. I would also suggest buying Andy Sabisch's Quattro/Safari handbook, It has a lot of good information it.
John