New tank setup- Rocks or bricks - fish hideout ideas needed for my new tank

Hello Alll fish lovers,
I have 6 tanks set up now and am wanting to get a new 125 gallon to
replace one of my 55 gallon tanks because my Fish are getting huge and
need a bigger place to live. I have used petco/petmart type purchased
rocks to give my fish places to hide and hangout and also several of
my tanks have slate in them which i build into castles or walls for
them to hide in and they all seem to love it.
My request is i am looking for a different type of rock or something
to build in my new tank so the fish have a place to hang out- I am
looking for ideas on what works good for tunnels or places to hide. I
have thought of red bricks purchased from home depot- you know the
type with the holes in the center so that the fish can get in there
and hide when they want to. I am looking for ideas on what to build
with so that i have places for the fish to go. Any thoughts on using
the home depot bricks? I have used river rock, slate,purchased pet
store rocks and am looking for ideas on something new.

What have you tired?

Thanks ,
Average_Joe