I have a black lab who won't bark at the door when he wants

Well, one way would be to not let him in when he scratches.

Because you let him in when he scratches, he learns that the way to get let in is scratching the door. He thinks that's what you want because it's what you reward/reinforce with what he wants (getting let in.)

So, in order to break his habit of scratching and train a new behavior, you have to stop reinforcing his scratching. Don't let him in when he scratches, no matter how much he does it. In the beginning, he'll scratch and scratch and scratch because he doesn't know why it's not working--it's worked all the previous times so maybe he just needs to do it more, he figures. But eventually he will learn that scratching doesn't work anymore, and he'll stop.

That said, in the process of him scratching the door and you not letting him in, he will no doubt get frustrated. It's not uncommon for a dog who is frustrated to whine/bark. If you can get him to bark on his own because he's frustrated, training it will be easy--as SOON as he barks/makes noise, let him in. Keep doing this and he will figure out that barking = getting let inside.

You could also train him how to bark on cue, and then cue him to bark before letting him in each time. In either case, if you do not want him to scratch the door anymore, you should never let him inside when he's just scratching the door.

>>2192440

OK thanks. It's kind of weird because my family had a dog that always knew to bark when we were younger and now our two new ones don't bark at all.

>>2192478
Eh, different dogs are more bark-y than others. Since your dog was more inclined to try scratching first, and he learned that scratching worked to get let in, he never had reason to try barking instead. If you teach him that scratching doesn't work anymore, you should be able to teach him to do a different, preferred method. Dogs are smart. If a behavior works to get them what they want, they will repeat it!