These are pretty much all my family has used for years and years - I honestly don't know how many we have altogether, but it's quite a few.
Some of our spots have had quite a few problems with trespassing, and my buddy had several stolen. To remedy this, my father had a section of square tubing welded by a friend between the two "spikes" at the top under the seat. He then drilled holes through these tubes front and back and top to bottom. We then run a bolt through the tubing into the tree once it's in place, which braces it further, and then we place a Master lock through the tube top to bottom, with the chain wrapped into it. You can't get the lock off to get to the bolt without cutting the stand in half. Even if the chain is cut, the bolt holds.
In 20+ years we've never had one stolen - we know some people have tried.
I can take pictures to explain if anyone is interested.