Teaching your dog to bark to alert you that he needs to go outside might be one of the most useful tricks you can teach and is much easier than you might think, especially if you have a very vocal dog! To teach a dog to bark to go outside, you must break the trick into baby steps. The dog must first be potty trained and also to bark on command. If you live in an apartment, with close neighbors, or currently or might soon have a baby in your home, you may want to teach your dog to whine or ring a bell instead. (We do not advise teaching a dog to scratch the door to go out- once you've had to refinish a door because of dog scratches, you realize there are better methods!)
Once you have a potty trained dog who knows how to bark on command you just need to help your dog understand the link between the behaviors in order to teach them to bark to go outside:
We don't advise using this method for already very vocal or high energy dogs. Once these dogs learn "bark" = "go outside" you may find yourself being woken up at 3am by an noisy dog who just wants to go outside and play! For these dogs, using a door training bell to give them the signal to go out is a much better choice, since you can either crate the dog or place the bell out of reach to guarantee quiet overnight.