We had seen this from the path by the pond, and assumed it was part of some rusting car, or machinery

Went up to check it out this afternoon, and it's a very interesting hoop. Very rough, heavy outside, smooth finish inside.
Then I noticed this fishline and hook wrapped around the hoop. Hard to see in the photo, but trust me it's there.
That's odd, I thought, but maybe it's some fishing rig. It's less than 100 feet from the water, after all. Then I looked down at the ground.
In between the blueberry bushes and leaves was what looks like a sea urchin, only all metal. Really spiky. An anchor?
When I picked it up I was impressed by the welding.
Then I noticed a small hole in one of the spikes.
Aha!
Now that's better.
Not sure if that was its creator's original intent, but I kind of liked it, so there it stays.
Should give the kids something to wonder about as they explore.