Ideas keeping a foster GSD busy?

Hiya. I foster GSD's for a rescue. This guy I have now was a stray, a gorgeous skinny 2 year old black and tan male. And I'm sitting her asking this at 8 in the morning because he's so active that I don't know what to do with him. Of course I'll take him on the runs and hikes with my other dogs but I'm looking for other ways to keep a huge GSD busy - both inside and outside the house. I'm looking for things to do outside and about, but also ways to keep his mind happy and relaxed while watching TV at night for example. Thanks.