Rewards Work Wonders. After the animals have both calmed a bit give them each a small reward, such as a morsel of some favorite food. Be sure to give the dog lots of verbal praise and affection when it is not barking or trying to get to the new animal as this will show the dog that you are accepting of the new pet's presence and you expect him to be also. Repeat this process several times over the course of a week or so, until both animals seem fairly accustomed to the presence of the other and their aggressions seem to have subsided. At this point, you are ready to move on to the next step and tip number three.
Get Help. This step will require an assistant to help with one of the animals. Have the assistant leash the dog and hold him firmly on a very short leash. After instructing the assistant to maintain control of the dog, open the pet carrier and bring the new pet out carefully. Your dog will likely move towards the animal so be sure the assistant has the dog held tightly and be careful not to let the new pet panic and escape your grasp. Gradually bring them closer together and let them calmly adapt to each others presence. Repeat this step several times over the next few days and by the end of the week, these two animals should be like old chums.
Another tip to remember in socializing your pets is that, while the animals most likely won't make an instant attachment to each other, there are those special picture perfect moments that you will want to cherish a lifetime. So keep the camera handy and loaded with film. The candid shots of training at its best provide memories that will last forever. Few things are more fun than looking at a picture of your dog with an iguana riding around the room perched on his back and telling a little white lie that you taught the two of them to do that.
Our final point is remember that just like humans, not everyone is going to get along. There will be days where the dog and the cat are going to feud or the iguana will get cantankerous and slap the dog with his tail for the fun of it. Some animals were just never meant to live in harmony but with a lot of patience and a little direction you can make your household fairly peaceable most of the time. When things go sour, just take it in stride and put the animals in their separate areas for a bit and, given a cooling period, they will be friends again in no time.
