I put sand in my run a few weeks ago. I clean it 2 - 3 times a week and turn the sand once a week. I noticed for the past couple of days that it is starting to smell. The sand has been damp and it has been cold so it hasn't dried out for a while now. I do not have a roof over the run so when it rains it gets soaked. Does damp sand start to smell and what can I do to fix the problem?