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Your dog's crate should be just large enough for the dog to stand up in, turn around, and lie down comfortably.  One of the reasons that crate-training is effective for housebreaking a dog is that dogs will not eliminate waste where they sleep.  If the crate is too large, the dog may use one end for sleeping, and use the other as a latrine.   If your puppy is still growing, you can buy a crate that will accommodate his adult size, and block off part of it with a divider (sold with some crates) to fill up the extra space. Many humane societies and some veterinarian's offices rent crates, so you can get one that is the appropriate size for your puppy and trade up as the animal grows. If you plan to use the crate for air travel, be sure to choose one that is approved by the FAA or your airline of choice. There are many different kinds of crates you can buy, including wire, plastic, and soft-sided.  Choose the best crate for your dog and circumstances.  Wire crates are the most inexpensive and breathable, and usually come with dividers for walling off part of the crate to accommodate a growing puppy. Plastic crates feel cozier to most dogs, and can usually be used for air travel. However, they aren't the best choice in hot weather as dogs that get hot easily. Soft-sided crates are lightweight and portable, however many dogs can chew their way out of them, and they can be difficult to clean. When you begin crate training, it is best to put the crate in a place where you and your family spend a lot of time during the day, like the kitchen or living room.  Dogs are social animals, and like to feel that they are part of the pack.  It is important not to put the crate in an isolated location, like the basement or garage. The crate should never feel like an isolating punishment for your dog.  You should plan to move the crate to your bedroom at night when training a puppy, so you can take the puppy out when it needs to go to the bathroom. Some dog owners simply set up two crates, one in the living area of their homes, and one in the bedroom. Place a blanket or towel on the bottom of the crate for the dog to sleep on. If you are using a mesh or wire crate, you can also drape a breathable blanket or towel over the top of the crate to create a cozier, more den-like atmosphere that  may help your dog feel more secure. Some dogs and puppies might mistake the bedding for something to chew on, or as bathroom material. If this is the case, remove the bedding and clean the cage, and proceed without bedding.  You can add it back in later as your dog matures. As you set up the crate, your dog may come over to investigate it.  Say positive things about the crate to show your enthusiasm for it, and allow your dog to explore.  However, you should not try to force your dog into the crate or close the door right away if he goes inside.  Getting used to the crate takes time and patience, and the more excited you seem about the crate, the more excited your dog will become.
Choose an appropriately-sized crate. Choose the right kind of crate. Find a good spot for the crate. Make the crate comfortable for your dog. Be enthusiastic about the crate.