Ever been in the forest and seen a big oak or some other type of tree laying on the ground rotting. Lot of the time if you look close you will find spikes or large nails someone used as steps years ago. I've used them before even used the screw in type when i was younger. When i turned 20 i went to work as a forestry fire fighter/forester and have been doing that for the last 26 years. In my time in the woods i have come across many trees like that, many times it will be cotton picker spindles used as they work very good for climbing steps. But the worst thing about using steel in trees is if and when they end up being cut for lumber or end up in a mill somewhere. I have been to a few mills around my home and i can tell you for certain that the last thing you want to do is to be close when one of these trees go through the mill. Its like a hand-grenade going off. So if you are going to use them use the screw in type and remove them at seasons end and get some caulking and close the holes up it will help keep the bugs out and will slow the dying effect.