Oils like citronella, lavender, peppermint, lemongrass and orange tend to repel cats when they smell them and are nontoxic. To make a homemade solution of these oils, mix one part essential oil with three parts water, recommends VetInfo.
Although best known as a mosquito repellent cats find the Citronella odour. I bought the Eucalyptus plus Mint essential oil at Walmart for $3.87 (large bottle).