"will work for food"

The pasture that the pigs are in used to be a junkyard in the 60s, and as a result, there's quite a bit of metal debris still remaining.  All of the stuff that will biodegrade in 50 years has done so.  That means that the vinyl seats and a lot of the sheet metal is just gone.  What remains are the larger, more substantial pieces of steel, like this wheel, engine blocks, axles and, of all things, chrome trim. 

The chrome trim is just as bright and shiny as it ever was, and it's pretty common to see a pig running around with a few feet of it.  They think it's cool.  But what I find really interesting is how much the pigs seek out the iron and steel. 

The pig in the picture is my main herd boar at this point.  He's 700lbs of pretty good natured boy.   He was walking along while I watched him, and then stopped, snuffled at the ground a couple of times and then dug this wheel out of the ground in 30 seconds.  No part of the wheel was visible before he started digging -- I think he smelled it.  Flipping it around a few times, he decided he'd seen enough and wandered off to do boar things.  (which mainly involves finding another pig and moving them for the heck of it.  "my wallow now, I'm the boar!" )

I'll periodically walk the fields and pick up the metal that the pigs have unearthed, and when I move the pigs to another area, I'll bring out the tractor and dig anything I can't get out by hand.  Over time I'm cleaning up the land. 

In the last 3 years I've removed 18 tons of steel from 12 acres.