Just like all other sponges they need dim lighting so that algae does not begin to grow on it and suffocate it. With out saying also it needs high water current. Also I found that sponges that are already attached to a rock do best. As far as the foxface goes, I would be worried it would pick at it. What other inverts are in there now? You might be okay depending on it's attitude now towards whatever is in there. What a splash of color to a tank though!
I have to agree with the above advice, high currents and low lighting is ideal. Algae will clog the pours of the sponge, causing it to not feed properly. It will turn white/brown in the infected area's. Speaking of clogging pours, any amount of air will kill it. Air will also clog the pours of the sponge. Make sure that there are not any air bubbles coming into the tank.
Most sponges you see have already touched air during one point of their shipping/handling process. Best if you bought them captive raised.
Graham
I read that they are difficult to have. Or with the low light high current and no air will they survive easily. Dont know much abou them but the color is great.
They are fairly easy to mantain(my opinion). Just remember to feed them. I had an orange one for about 4 years. I would just feed it DT's from a turkey baster and it did fine. It was a slow grower but did fine. I decided to move my tank and place it in the wall. When I did I let the sponge touch air and that was it, within two months or so it was dead. Follow the above advice from people and you should be fine.
Chris