Best option for property protection

We have rental neighbors who continue to drive on our property & run over planters & plants at edge of boundary. Steel pipes filled with concrete was the best option suggested by salesman from Dixieline building supply store. I thought may a brick retaining wall planter which would raise the concrete planters 3' off the ground & protect them but he said they would just break down the wall with their trucks. If have also thought about placing large boulders between the planters. Wife says we are just going to have to wait till they move because they park 6+ vehicles in a space for 2 and anything I do would only cause them to park on the street with limited parking now. My plan is to put drivable paving stones in my yard 4 2 cars & then the steel poles. My grandfather would have used shotgun & rock salt