i put two more 4x4s in the front yard because the stupid neighbors won't stop driving through the front of my yard to parallel park in front of their fence. i put 36" in the ground and 12" above ground with red reflectors all the way around.
if they hit the posts and tear something off their car, tough crap. if they pull them out, i will go to 10" schedule 80 pvc filled with concrete and rebar, like i did for the mail box that time. i asked the multiple times to not drive through the yard and spoke to the landlord about it. neither care so we get to play rougher now. i already spoke to the police too, their answer is to get them on trespassing. i like physical barriers. they actually stop stuff