Nikko is constantly digging at my floor!! Apparently he thinks he's going somewhere because he digs with such passion!!

It gets really annoying sometimes and I tell him firmly to stop but he just ignores me and keeps right on digging. He digs on the sofa, on my hardwood floors and even in his crate. I know this is an instinctive behavior in terriers but how can i get him to stop being so destructive?