I have had as many as seven in my yard. There is something called deer away or deer off and I am told it works like a charm. It lasts for about a month and then you re-apply it. It must work as my neighbors have salvaged their yards and the deer come over to mine. They love day lillies, apple trees, azaleas, and hostas among other things.
My neighbor across the way has put a large-hole netting over her plants and that seems to work also. It is black and disappears into the scenery. She also put aluminum pie plates hanging from strings too. That is not nearly as attractive. Cord strung low in front of the plants works also as they brush up against it and it makes the deer nervous. They cannot see it. Just don't forget it is there and trip over it.