There was another discussion on it here.

 

I live in New Mexico, so cholla is everywhere I have a large piece in my tank. Like one of the posts in the link Tazman gave you said, my fish also love it. They can go inside the wood.

I would be a bit worried about getting a piece from a craft store, only because you don't know what treatment they've done to it. If you can find out that the company that sold the wood to Michaels' has not treated it with any chemicals, I would boil it, on a slow boil, for at least a half hour. It will try to float at first, but will eventually get water logged and stay down. I used dark thread and tied java moss to it, until the java moss stays on by itself. You can also stick roots of java fern in a hole and java fern will do fine on cholla.

Best of luck. I've had mine in the tank for about a year now, and have no problems at all with it rotting or anything. That's my experience.

Gwen