Need advice on a good hide for Cuban tree frog

[NancyC]

My Cubans are only 3 months old. They like to pin themselves in nooks and crannies. They have been small enough to wedge themselves between the glass and stick on thermometer but now they are too big.
So I put in a bromeliad and look

That works for now but they are sure to outgrow that too. I am just trying to plan ahead. Here is my tank set up now. 18x18x24.

Any good ideas? I know Cuban tree frogs are known to wedge themselves in cracks. How do I create that in a tank?

They are growing so fast.