Thorny Ground Cover for SW Michigan Zone 5B
Having problem with inconsiderate dog walkers letting their pets do business in front of our bushes. I would like to plant some thick, thorny ground cover to discourage this. In California I have Carissa that does the trick very well, but it isn't hearty to SW Michigan (New Buffalo area). Can someone recommend a nice thorny ground cover that is hearty for SW Michigan Zone 5B?