My large outdoor enclosure has a dark muddy spot under an upper deck hide box. That being said, my 3 adult redfoots try to race to that dark muddy spot to lay in a mud hole that they wallered out. It is very wet and muddy under there. My fear is that too much of that will result in shell rot later down the road. My question is should I close that spot off or just fill in the muddy are with cypress mulch or something?