6 Answers

A long lead, I had a dog similar to that, I had her from a pup,tried everything but nothing worked, it's an "alpha dog" thing, they don't want any other dog encroaching on their territory.

Our dog does not like any other dogs. We live in the country so no problem. He really likes our cats and plays and cleans them.

How is your friends dog doing now Dave?  I read a good article today about socializing dogs. Send it you your friend if you wish. 

http://www.whole-dog-journal.com/issues/4_12/features/Teaching-an-Aggressive-Dog-to-Socialize_5417-1.html

I'd suggest your friend be VERY careful when there is another dog in the vicinity. The dog at my house does not get along with other males, particularly of the same breed (bulldog) and my son had to give away HIS dog (mixed breed) to move his wife's deceased brother's pit bull (a big baby and wonderful with people and the kids), who does NOT get on with ANY other dog. 
Were it my new dog, I'd respect the information and keep the dog away from other dogs.

That is bad advice Dave,Read the link i gave you,and scroll down to the 9th myth,does not matter how old the dog is,with proper effort and time,any dog can be trained,,have a read and let me know what you think..>>>>>>>><<<<<<<<..https://apdt.com/pet-owners/choosing-a-trainer/myths/

First of all, Sunny, it is a German Shepard, my miniature Dachshund unprovoked in my back yard was mauled badly by a Shepard, obviously this breed likes little dogs to fight with, i regard them as a 'Cowardly' breed, i doubt his personality will ever change.