There are quite a few recipes for DiY rock floating aorund RC, reefs.org, and garf (the OG aragrocrete mix). Any one of the longer standing ones can be used and deamed safe for attaching rocks to each other.
The problem with anything other than the hydraulic cement, is the time it takes to cure them. Most take a few weeks if soaking before the pH balances out, but the stuff Dave mentions only take 24 hours.
Ive thought about using a portland cement based mix, and thought about using one of the quik crete mixes. They are both available at Lowes/Hd, and are fairly cheap.
I also like the spray foam methods that have been floating around. I know that stuff is strong, safe, and easy to work with.
Heres my favorite thread on the subject
http://www.reefcentral.com/forums/showthread.php?s=&threadid=1184780&highlight=spray+foam
This stuff can be put in the tank a day after epoxying. Its the most appealing to me as its cheaper, lighter, and easier to work with compared to the 'crete ideas. I also have most of the materials needed for doing somehting like this.
Drilling is something ive never had luck with either Rick. I think they wire tie/eggcrate/foam would be easier to make look natural as well. Ive mentioned before how much better it looks when the rock is elevated within the tank. But, while Sanjay's and the TOTM are beautiful set ups, they arent natural looking enough to me. You would never find pillars/structures shaped like that on a reel reef. Everything would be held in plale by gravity, and thats what I prefer in my tank

A little epoxy/foam/crete to stabilize things isnt a bad idea though, and can make the structures a lot more interesing/fluid than just the typical stacking.