Dogs and particularly cats can destroy a planted garden area in your landscape, not only using the soft, moist soil to deposit their waste, but frequently by lounging among and on top of plants. Repellent sprays are expensive, and fencing the area is not always practical or possible. Growing plants that are particularly offensive to dogs and cats as borders or as companion plants can deter your pets from areas you do not wish them to enter.
The oils and fragrance of many herbs have a distasteful scent to cats and dogs, which will cause them to avoid the area. Dogs and cats do not like citrus smells, and many homeowners will spread the peels of citrus fruit throughout the garden, but lemon grass is much more attractive and can help keep your pets out of the area. Lemon grass is an attractive ornamental herb that contains a high level of citronella, a natural repellent to a number of insects as well as cats and dogs. Anise also emits a fragrance that is unappealing to dogs and cats and will repel them from your garden.
The pungent smell of marigolds, particularly Mexican marigolds, will keep your pets out of the garden and send them looking for an alternative place. Calendula will have a similar effect. Coleus plant varieties such as "Scaredy Cat" or "Dog's Gone" have a distasteful odour; planted among other plants or no more than 90 cm (3 feet) apart will repel your cat or dog -- and maybe you, too. Bergamot and rue, both hardy perennials, also are known for repelling cats.
Shrubs, especially thorny shrubs, will keep dogs and cats away from an area because they prefer not to go through the shrubs. Roses, raspberries, barberry and holly grow densely with thorny stems. Dwarf citrus trees or shrubs and ornamental mock orange shrubs emit the citrus fragrance that repels cats and dogs.
Since a main attraction of your garden is the loose, moist soil, growing ground cover may keep your pets from injuring your plants. Like shrubs, thorny ground cover will be unappealing for cats and dogs to walk or lay on. Crimson pygmy barberry is a low-growing, ground-cover-type plant that has tough, sharp thorns. Dwarf Euphorbia "Crown of Thorns" are thick with thorns in addition to being a low-maintenance ground cover. Sedum and other thick, dense covers that completely cover the ground, making the soil inaccessible, can keep cats out of the area.