Do you have spots in your backyard where the surface goes from one level to another, such as the edge of a verandah? Use plants as visual indicators so that people don't trip.
Sunset Magazine explains:
Tuck a small row of echeveria between an upper and lower patio to remind visitors to step up. Use larger succulents, such as the three kinds of aeonium pictured, to signal where the upper patio drops off.
While they mention specifically using succulents, you could use other types of plants that may suit your climate or backyard better. Just make sure they will be visible during the seasons when you'll use your yard. For more ideas on how to landscape your yard or garden, check out the full post linked below.