I have a large spring mounted to the top of mine with a ball fastened to the spring. It actually works, but new balls need to be added every once and awhile.
As it's been said, make sure it meets County or City code for being break away. I was an expert witness to a lawsuit where a snowmobiler was killed where he hit a wood fence post that was in the ROW. The attorney had a heyday. It didn't end well for the land owner.
Funny story. Growing up we lived on a road with no berms and between the plow trucks, fast cars and mailbox baseball we had to replace mailboxes often. I remember our neighbor screwing a big soup can to the bottom of his new mailbox and setting it on the post. Every morning he would carry the mailbox down the driveway and put it on the post, every afternoon he would carry the mailbox back to the house. I can't even tell you how many years he did this, but I'd guess 15. Lol. Here at the compound, our road is rural but many miles long and cars FLY! Sometimes literally. Again, no berms. There's been around 75 wrecks in front of my house (in 25 years). Every mailbox, sign post, and telephone pole and a porch has been mowed down. There's a bit of a blind hill and slight turn and people that aren't familiar have trouble with it. You can easily negotiate it at 60 mph (the speed limit is 40) ive done it at 65 just to see. Years ago i brought home an old fire hydrant (for decoration) and set it next to my driveway. (First time it got hit it busted a motor mount off a nissan and ripped the back bumper off, blew the tail lights out and popped the trunk open. Car continued another 100' across a ditch/drainage area jumped off a little bump and broke a pole off 14' up and landed 150' past the pole. I'd guess the car was going 80+) The fire hydrant was fine. only broke the 4" cap on the front. Its funny, the fire hydrant is famous here in the valley. There is no city water. When my neighbor called his insurance co a couple years ago, the agent said, oh, you're down by the fire hydrant.
My current house was my grandparents house since they built it in 1976. My grandpa would cuss up a storm at the road maintainer who would hit the mailbox post EVERY time he graded the road. Grandpa finally gave up and put a piece of 4” pipe inside a cream can and filled both up with concrete. He then welded a piece of 1/4” thick square tube on top that the mailbox slides into. It just sits on top of the ground, but the road guy hasn’t hit it since. Someone knocks it over a few times a year, but I can just go set it back up and not have to repair anything.
