An angle grinder with a cut off wheel, or probably most hand saws will make quick work of most rock. I was able to cut straight enough to make pedestal pieces that could be siliconed to the base of the tank. Since I'm going to run a sand bed, I cemented my pedestal pieces to flat pieces of landscaping rock that will be buried under the sand. Having said all that, in retrospect, I should have just bought the pre-made pedestals.
If you have it well planned out though, you should be able to do the work you need to before you have much die off. Also, no reason you can't use a masonry bit in an inch of water, so long as you're very careful or using a cordless drill. Ever take art history? Contrapposto. If your creation balances by itself without fiberclass rods, zip-ties, epoxy, superglue, it will inherently be pretty stable and won't unduly stress whatever method of bonding the rock you choose to use.