Teaching a young dog new tricks?

For Finley's first few weeks home, we brought him out the front door to go to the bathroom because the back deck was covered in three feet of snow. Now that the snow has melted and we have a fenced in area in the back, we bring out there. But poor Finley still goes to the front door and whines to go outside (even though we pick him up and bring him out the back). I wonder how long he'll be doing that?