Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Wurger's idea of using iridium, the 2nd densest element: 22.53g/cm3 is an excellent one if you are willing to shell-out $635USD/ozt (troy ounce: 31.1g)
I still say gold is the way to go...not only will it keep your rig on all 3 points, but it's a clever way to stash your investment where no one would think of looking...