What kind of dogs?
Some dogs really need bones and some could care less. I give my big dog, who is a chewer, bones quite often. I try to change around what I give him.
Nylabones are great but all my kids favorites are the *real* bones. They come in all different sizes. I also give the occassional rawhide (I know some people don't).
Sometimes anything other than their dog food can upset their tummies. Watch what you've given Ollie and if it happens next time you give him the bone, then you'll know. It very well could be possible.