Rock hides and tunnels
Ohhh, I remember seeing that cave hide in your other photo when I was looking at it. I also saw the exact same thing, or something very similar to it, at a pet store believe it or not. Yeah, that could do. If you had a tray large enough for the whole hide to sit on and that could collect the water so it doesn't get into the substrate in the rest of the terrarium, you could sink the tray part way into the substrate, fill it with cocofiber and put the hide on top of it. I don't know exactly how well that would work but it is worth a try. Are you sure there is no more room in the terrarium for one more hide?
And I forgot to comment on the tunnels inside the log thing you mentioned. It is not so much the ends of the tunnels you need to worry about because leopard geckos are perfectly capable of backing up out of dead-ends like that. I would worry more about your gecko getting stuck mid-way. If some parts of the tunnels are more narrow or more unevenly shaped, your leopard gecko could get itself wedged inside the tunnel and not be able to get out. If that happens, you may need to go as far as to break the log structure apart to get your gecko out. To make sure this doesn't happen, see if the tunnels start to widen at some point inside. Try rolling a very small ball like a marble into the tunnel and see if it rolls all the way to the end of the tunnel without getting caught somewhere. Try this with the structure upside down and on its side too, to be positive. If the tunnel just gradually gets narrower the way a hollow animal horn does, then it won't do this and you won't have a problem. Or you can always get rid of the log structure if you are still worried about it.
@ Allee: Wow, I had no idea those circular thermometers were so inaccurate :shock: I have one of those in Pepe's (my white-line gecko) terrarium and I always get these unusually high temperature readings. A lot of them are in their 90's and one time it just about went up to 100 degrees. I had been wondering if those were what the temperatures in there really were or not. Hmmm, time for some experimentation...