How to protect seeds and plants being planted in our greenhouses from critters this winter.

Good evening folks! I've witnessed some holes and stuff being dug out by critters in my seed trays at my greenhouse today and had seeds being dug out and eaten. I don't know how that happened. How can we protect our plants and seeds planted in our trays from rodents in our greenhouses this winter? Could sealing the tops help keep critters out? And how we give plants some air while protecting them from being eaten? Please let me know in the comment forum. Good night!

Well I decided to buy some netting to cover my newly planted seeds with, tucking it under the containers or holding it down with rocks etc.  This is outdoors, but the problem is comparable, I can't let Sandy the squirrel do again what she did in Aug./Sept. when I planted seeds for hopeful autumn harvest, I need to keep her out until things are growing.  I'm planting soon, so hopefully it will help.  With a greenhouse I'd say the same idea on a smaller scale?