Why can't you leave him in the yard with his toys when you're away or busy with other things.
no, because dogs shouldn't just be left in yards unattended. IMHO. it would only take a few minutes for a bored dog to dig under a fence. i would never leave my dog in the yard while i was at school, i would be worried sick but maybe that's just me.
Leave him outside, he will be fine, a big bone, peanut butter in a kong, a few chew toys and he will be fine.
Just make sure there's shelter and plenty water lying around.
Besides a pup will sleep 3/4 of the day anyway