Frozen food is very good. I usually give my dogs raw bones/marrow bones and meat with bones that I find cheap. Turkey necks are also very good for keeping them pups busy for a while.
I'm kinda scared to give my dogs toys alone, especially in a crate where they can easily get very bored. Chew and eat a rubber toy, isn't good for a dog stomach. You can get the same problem with bones too, but they are probably easier to digest, than rubber/plastic.
And remember, always feed RAW bones, never cooked! Cooked bones splinter easily, and can tear up a stomach … good to remember. 🙂
