Land mines?

We are in the process of getting a fence put in our yard.  This is John outside with a survey crew finding our property lines.  One of our neighbors saw them outside and ran over to another neighbors house (the one we are finding the property line with) and said, "Dude, there's an army guy in your backyard with a metal detector looking for something.  Do you have land mines in your backyard?"  

No, there are no land mines in our backyard.  We are simply trying to put up a fence.