Why can't I use reptile decor in aquarium?

Are you using wood in one of your brackish tanks or a SW tank?

Right now I have a mudskipper tank with a few fake plants, sand banks, and a couple turtle docks. I want to add some additional decor for them to crawl on/hide under, etc, as well as make it look more natural so i wanted to add some wood - either fake or real. As far as real wood goes, driftwood breaks down in saltwater and the only wood that will work acceptably is Mopani wood. The problem is it goes for $50-$80 for a relatively small piece and I haven't yet found one that is worth me spending that much.

All of the fake decor made for fish tanks have open holes all over it to allow it to fill with water. This is cool if the item is fully submersed but with mudskippers, I am afraid they will fall in a hole and not be able to get out since the piece won't be submerged. There are tons of great perching type decor pieces built for reptiles, but they all say not to use in fish tanks.

My other tank I just setup brackish and am getting it ready for a puffer. I spent like 50 bucks on fake driftwood and stuff so I am hoping that it doesn't fall apart..
 
AquariaCentral.com