Adopting an adult dog
Adopting an older dog instead of a puppy gives you a better idea of what you're getting. Puppies of unknown breeding may present many problems down the road including major health problems.
When you go to look at an adult dog for possible adoption at the local shelter, remember that what you see is what you get. A shy, cowering dog will take just as much work as an overpowering, in-your-face dog.
Take the dog you are interested in off to a quiet area away from the confusion to evaluate his behavior. Ask the shelter worker about the dog. Look for a dog that will come up to you, one interested in interacting with you. An aloof dog will most likely remain aloof. If at all possible, family members should meet the adoptive prospect, even the smallest child. If the dog shows any fear or aggression to anyone, stop the adoption process and look further.
When you bring your new dog home
Establish a safe area for the new dog that will keep him AND your house safe. The safest way to do this is with a crate.
Most shelter dogs spent a lot of time in a cage, so the transition to a crate at your home should run smoothly. A confined area such as a crate will greatly assist with potty training and give the dog a safe, comfortable place. Time in your house outside the crate should ALWAYS be supervised for several weeks to several months, depending on the dog. The only factor regarding supervision or lack of is your observation of the dog's behavior.
Feeding should be in the crate at first, as well as daily times in the crate even while you are around. Dogs quickly learn when they are crated only when nobody is at home, and some can develop separation anxiety. No matter how old the new dog is when you adopt him, he should always be treated like a puppy and not trusted until he earns your trust. You have worked too hard for your house and the stuff in it to have it destroyed by a rescue dog!
No matter how old the dog is, potty training should follow the same pattern: outside on leash, with voice command to eliminate, praise during elimination and freedom in the house only after elimination outside. The length of time you will need to do this depends on the dog, varying from days to months.
Enroll your new adult dog in obedience class
One of the most important things to do with your new dog is to enroll in an obedience class.
This class is important for many reasons. First, it establishes a working relationship and bond between you and the dog. Next it socializes your new dog to other people and other dogs. It also helps reinforce basic training, even if the dog seems to already know many of the basics. An finally, it helps teach the dog that he must comply even with distractions.
Don't make excuses for your new dog! You may observe he is shy around men or strangers; many people think the dog was abused before they got him. He may have had a scary experience, but generally, if you don't know for a fact he was, he was probably just under socialized. To sit on the excuse, "Oh, be careful with him, he was abused as a puppy," is an immobilizing thought. Instead of carefully avoiding things that frighten your dog, give that man/stranger an irresistible treat to give to your dog every time they meet; you may be able to work through the problem! What may have happened in your rescue dog's past doesn't need to cripple him for life! Obedience classes will go a long way at helping your new dog overcome many of the problems they may have had in the past.
Have your new dog checked thoroughly by a vet
Unless you work closely with a shelter veterinarian before the adoption, the first trip after acquiring your new dog should be to your vet. Evaluate health issues before he establishes himself in your home and heart.
The vet will check a stool sample (take a fresh teaspoonful with you in a plastic bag) for intestinal parasites, do an overall general exam, and check for heartworm (if he is old enough). The vet will also evaluate his vaccination history (which you also need to take to the appointment) and give him any vaccinations he is lacking.
Introducing the new guy to other pets
If the potential adoptee has a problem with pets you already have, that dog should not be going home with you.
Part of your pre-adoption evaluation should be to observe how your dog-of-choice interacts with other animals. Ask shelter workers what this dog is like around others. Check for yourself. With the help of a shelter worker, introduce another shelter dog to your dog. How does he interact with the strange dog. If you have a cat, ask a shelter worker to bring out a cat who tolerates dogs. Some shelters will allow you to bring your pets for an introduction, others may require it.
You will still have to invest time in introduction and supervision of the new dog and existing pets. The new dog should be on leash and your existing pets should also be controlled in some way. With a cat a carrier is a good idea. Don't try holding the cat to make the first introduction. Other dogs should be on leash and introduced one at a time. Raised hackles are normal even in friendly introductions. Keep leashes fairly loose or leave dragging on the ground, but always be ready to pull each dog away from the other should an argument ensue. If a fight starts, never put your hands anywhere near to pull the dogs apart. Throw a blanket over them or use a chair to separate them by wedging in between. These introductions work best when one person only handles one animal.
The new dog should not be alone in the house with existing pets until you have carefully monitored and controlled interactions for a period of time. That time period could be anywhere from a couple days to a month or more. The new dog should be crated when you're not able to supervise. The crate can still be in an area where your existing pets can approach to sniff. However, this needs to be supervised. Existing pets could tease the new one and the new dog may be overly protective of its cage and lash out.
With careful planning, preparation and training, adopting a shelter or rescue dog can be one that will work for life.
Checklist for adopting
Think your choices through. Don't rely on your heart strings no matter how tempting.
Make sure the new adoptee will work in your home including with other pets, men, women, children.
Consider why you want a dog, and why you want a shelter/rescue dog. After all, the idea is to have adoptions work and not become future problems.
Do you want all the extra work that comes with a new puppy? Or would you rather start with a dog that is a more mature?
Don't adopt with the idea that you can change a dog that exhibits bad behavior. You'll be able to work with what you have, but generally a dog is the way he'll be.
Don't hesitate to engage the help of an experienced behaviorist or trainer to help ease the adoptee's transition into your home and your life.