My 10 month old German Shepherd is a service dog in training and has started guarding his dog bed and becomes defensive to anyone outside the family, any advice?

Many herding/working breeds start to show this type of behavior in adolescence and it's quite normal for many GSDs. In what situations are people from outside your family approaching him on his bed and why? How do you respond when he does this?

I would be concerned about having a service dog prospect with this tendency especially if you will need this dog to work in public venues.

We've bred, trained and lived with working GSDs and Malinois for over 40 years and they are 2 breeds that I usually deter people from raising as service dogs unless the owner is an experienced service dog trainer and the dog comes from a line of dogs bred specifically for these tasks (i.e. Fidelco Guide Dogs) Some of the strong protective, territorial instincts that come natural to GSDs make service work difficult, if not impossible, depending on the experience of the trainer and the tasks the dog will need to perform. Some dogs are fine in certain settings and struggle with working in public.

With all that said I would suggest you find a legitimate service dog trainer and get a one-on-one evaluation since I can't advise without seeing you and your dog in person. I wish I could but this is a more complex issue based on his potential career as a service dog.