What do you use...

CAPSLOCK

Elite Fish
Jul 19, 2004
3,682
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Cape Cod
#2
I just stack it, as long as the fish aren't too big/boisterous they won't knock it over. I've also done this with small caves in FW, nice smooth rocks, too. Just set them so they are stable.

You want to stack it right on the bottom glass of the tank, then add the substrate afterwards so if they dig in the substrate they can't dig under the rocks and cause them to fall.