Maybe he got hurt in the process?
If the blood is good, and no fever, he should get back on the tracks, as long as he eats and drinks. Does he poop okay and no blood in it? One trick is a little oil, - human feed oil for cooking. Have him drink like a couple of ounces, and make sure he is outside afterwards!
For sneaking medicine in, well, he ate rocks! But seriously, butter, pate or a slice of burger....a rock-eating dog is most presumably quite a gobbler.
11 years for his breed, isn't that rather old BTW?