You are not supposed to get a dog for the purpose of entertaining your current dog, you are supposed to get another dog because YOU want another dog. Your current dog already had a friend (you) and your current dog should already have been getting entertained (you.)
I have never heard of the "3 year rule" between dogs but I am guessing they said that because your dog is not physically and mentally mature until 3 years of age. Some dogs are friendly with other dogs when they are young but then when they mature things change and they no longer tolerate other dogs. So if you have 2 dogs close in age when they mature they might start fighting. It's also not a good idea to get a puppy when you already have a young dog because they can take a couple of steps back in training or they can pick up bad habits from the new puppy. Also when the dogs get older you will have 2 seniors at the same time and seniors are EXPENSIVE and you could also lose them within months of each other and that is double the heartache.
Originally Posted by scarfish
the best decision i ever made was getting a new puppy for my 1 year old
Sinister ~ black GSD 3.11.09
Draven ~ Dalmatian 6.30.13