Got the acrylic rod today and made two good size rocks into one larger more stable rock.
Here are the two rocks I started with.
And here's what it looks like now.
I shot this with the flash which caused the acrylic rod to shine like that....wont do it in the tank.
Here are two back to back shots at about the same angle....one w/ flash, one w/o
Right side...you can see where the rod was inserted
Rear
Left side
Top
The rods all but disappear when inside the tank and any sort of algae starts to grow. I just used regular masonry drill bits and drilled through the rock. This is pretty porous and IMO, soft rock. I have some nice pieces of rock that are denser and harder, and they dont drill as well....in fact, they have a tendancy to shatter and break when drilled. From what I've been able to determine by screwing around with some less attractive/less usable pieces, is that drilling holes partially through the dense rock is doable, but as soon as the drill bit begins to pass through the back side of the rock, it shatters.
I also have a Lava rock that is almost impossible to drill through....so for these pieces, I'm waiting for the Thorite to make the racks...