We use a website connected to our county accessors office to find out who owns it. We actually ask the guy who is in an investment group that owned the property. We have a general permission to metal detect all that groups empty lots. This group buys up dilapidated housing and tears it down to get rid of some of the blight in the area. Depending on the area something eventually goes back up in it's place. Of course the worse the area the longer it will be before being reclaimed.
We hunt many tear down lots. Actually that's where a good portion of my silver has come from. Another couple of corporations has bought up and torn down many houses in older parts of town. Some we just hunt without asking as no one has ever said a word to us about it. These are as I said a corporation or investment group owned, not by a single individual.