Concrete to bond rock?

[Delphinus]

I don't have any good recent pictures. I did put up a before/after 7 years thing on IG about a year ago. I can't seem to link to the photo itself but the link to the photo is here: https://www.instagram.com/p/BeLw8owDHHf/

I do agree with the rod idea. It's hard to tell in the picture but the rock structure on the right is a bit of a floating over hang with a large cavernous area inside that the fish love to hang out in and sleep for the night. I did this with rocks drilled to accomodate a rod, and then zap strapped onto an acrylic base hidden under the sand that compensates for the otherwise uneven weight distribution (the overhang is pretty large).

I think I actually used fibreglass rods actually now that I think about it. You should be able to get both acrylic and fibreglass at IPP, but FWIW you can also get fibreglass rods at Canadian Tire. They're like driveway or parking lot markers for when there's lots of snow and you need to mark out the edges so you know where not to drive the snowplow. They have little reflectors on the top, just hacksaw that off.