can be either biological or chemical. This type of repellent keeps deer out by filling the entire area with a strong odor.
A few odor repellents don't smell bad including shredded deodorant soap and garlic, but most biological odor repellents are gross and they smell horrible, including Milorganite, lion and other feces, fermented blood, feather meal, and bags of human hair. Note! Predator urine is also sold claiming to repel deer. This urine is often collected under the most inhumane conditions so predator urine should never be used. Additionally, predator urine is not an effective deer repellent.
Chemical odor repellents are noxious and dangerous for humans. Chemicals sometimes used are moth balls, lime sulfur, Thiram, creosote, nicotine, ammonia, and many other compounds. These chemicals are toxic.