Neighbor strike again

Concrete planter were placed along drive way because neighbors would drive on our property. Reflectors were placed in the planter but they were stolen. Sober or not they are collectively the worst group of drivers I have ever seen in one place. Now the 2nd concrete planter has been run over and broken out of it's concrete footing. Now I have to figure our what to put between the plantar that are higher than a truck bumper that will look good and protect the plants from swinging doors and bumpers. Decorative rocks, large 3' sections of tree trunks, steel poles or concrete poles. That is the question