Rock Stacking

I'm looking at redoing my aquarium landscape to use some larger rock and stack them up into a kind of wall in the back of the aquarium, similar to some of the tanks I've seen people post on here. I've fooled around with this a little bit in the past and had some problems with fish trying to swim into the small cracks between the rocks when they get spooked and firmly lodging themselves in there. Is there a way to free-stack rocks like this so that the fish will be safe?

Here's a good DIY guide that would produce a tank that wouldn't have that problem: http://www.cichlid-f..._background.php

Free-stacking is a bit dangerous, not only because of the problem you mentioned but also because of the possibility of rocks falling, crushing fish or cracking the tank. Either use a foam background like the one in Erica's link, or stick the rocks together with expanding insulation foam (you can get a black version from pond suppliers). This will also eliminate any unwanted crevices. You can always cut the rocks back apart if you want.

I"ll never forget the day I was working in a fish shop when a well liked regular customer came in with 3 buckets containing his prized african Cichlids, all large, all valuable, all maimed and soon to die from flopping on the floor too long. He was in tears. He wanted me to put his fish in our tanks, which I did, but none survived.

During a water change when the tank was half empty, he lifted one rock to siphon around and it slipped from his grip and went through the bottom.

Be careful not just how you stack them, but also how you move them.

I really prefer the look of natural rock to styrofoam. And I'm a college student. A project like painting and cementing styrofoam isn't something I have the time or the room to do. What if instead of stacking rocks all the way up the back of the aquarium, I more pile them up in the corner where my filter intake is to hide that, packing sand in between each rock like bricks and mortar; more of an angled wall (much wider at the bottom than the top) in one corner than a precariously-stacked rock background, and then maybe a little catfish cave in the other corner (nothing fancy, just a dark spot they can hide. Any thoughts on this?

The sand will not stay. I really think you should take a look at the expanding foam, just to glue the rocks together. $20 and a few minutes' time is well worth the peace of mind in my opinion. http://www.aquaticec...117/Rockin-Foam

Look into the red tuffa rock they sell in pet stores. It's much lighter than most rock and is porous enough to serve as potential biofiltration media.
I don't mind the look of it, specially when the brown diatoms cover it. I've had 100gal tanks stacked end to end surface to floor with enough hidey holes for 3 species of mouth breeding Africans cichlids to keep up self-sustaining populations for years. Never had a leak or mishap [they don't slip through your fingers like algae coated cobbles ].

If you don't like the look, use it as foundation to build up bulk then try and hide it.

Buying it by the piece would be a very expensive bad idea. Watch for tanks for sale ads that list it. People breaking down tanks don't want to sit on that ugly rock. Pet shops going out of business is another unfortunately productive source.