I do a fair amount of sawing, both firewood and maintaining family land. For the big stuff I use a large Husqvarna Pro model and cutting into fence staples, nails, barbwire and other farming type metals is common. Anything of size just dulls the chain on contact. Sometimes it makes me hot under the collar to say the least.
But the strangest thing I found in my own yard. It was a plow tip buried over halfway deep in the top of a fat lighterd stump. I think many years ago this land was covered with pines, some quite large, so to create more cropland some one cut all those trees off about a foot under the ground. And later while plowing with a Georgia mule they hit this one large stump and really drove it in deep. Unfortunately for me, even fat lighter will rot over time leaving a hole where the wood once was. In my case many holes and depressions began showing up. I took on the project of getting them all up and filling the holes with dirt, this is when I found the plow point.