You forgot one.

They JUMP. A bored GSD will jump your fence...you need it to be over six feet high. Or just don't let your GSD get bored. There's a reason they're good agility dogs.

My brother-in-law has one and lives a stone's throw from the Canadian border and I joke about him going over the border if they make him mad enough.

(Now, if you want to have fun, there ARE high jump competitions for dogs and GSDs do well at it).