Dig a trench approximately 10 inches deep around the edge of all four sides of your bed. Stand chicken wire in the trench. Attach to a one-by-one-inch post at each corner. Fill in the trench, compacting and tamping down the soil. This will keep out digging animals such as groundhogs. If your problem is moles and voles, use a finer wire but follow the same instruction.
Lay dog hair, onions and/or talcum powder around your hotbed frame. The smell of a dog will often be enough to deter moles, voles and rabbits. Cat fur can also be used. The hair can be collected when groom the pets. Surrounding your hotbed with onions will deter rabbits. Sprinkling talcum powder around the frame will keep animals away as they do not like the feel on the talc on their feet. The talc should be reapplied every three or four days or after a rain.
Lock your hotbed to keep clever raccoons from opening the lid. Deer are not usually able to gain access to a covered hotbed but if it's left open, they will help themselves. Surrounding your frame with human or coyote urine will be enough to discourage deer. Electric fencing will discourage larger animals but is not effective with anything smaller than a raccoon.
Put three jalapeno and two habanaro peppers in a blender with enough water to create a mix. Strain through cheesecloth, add two drops of dish-washing lotion and 2 tbsp. of cooking oil. Use one part concentrate to 10 parts water and spray around your frame. This works with any animal pest and is an inexpensive, natural remedy.