As nearly everyone else has said, topless is best for a rack - that sounds so dirty, LOL. One of my racks has to use lids, and it's a real pain in the butt... water dishes are always spilling, and I have to remove tubs completely for everything (cleaning, removing snakes, etc). I tried to remedy the situation by using furniture sliders to prop the tubs, thus eliminating the need for lids, but the snakes took advantage and managed to escape. My big girl even figured out she could push the tub, giving herself a nice gap to squeeze out of. So not only do I recommend topless, but also the front-loading style (as opposed to side-loading, which is what Mona escaped from).