You should never give a dog a real bone because it can splinter as he chews it and result in choking. There are special rawhide and other types of bones available at pet stores. You can give your dog one of these bones but be aware that dogs respond differently to these playthings. Keep an eye on him and make sure that he isn't at a risk of choking on it. If your dog tries to immediately eat or destroy a bone that you get from the petstore, it may be that you need to find other ways to entertain him. It's best not to leave him unsupervised if you have given him a new chew toy or if he is overzealous in chewing - for his own safety. Also, if your dog is territorial, you shouldn't encourage him to guard a bone. Sometimes even very gentle dogs can become aggressive around something they don't want to part with. Be aware of this and don't take any risks with your safety.
It's good to give him bones; that's always a nice treat for them. Maybe he just enjoys relaxing; lots of dogs are like that.But you could get him some toys to amuse himself with..perhaps a tennis ball to roll along, and some squeak toys, some good sticks to gnaw,and anything else you'd like him to play with. you should leave the dog in a garden where possible, then he will be stimulated by birds and will be able to bury his bones and roll in the grass and mud, which most german shephards love. Hope this helps.