Just have Oda have men holding a sign(that only modern people could read/recognize) in every village surrounding where the guy was spotted.
He would probably be thrilled to have the chance to have another expert of modern technology under his control before anyone else gets them.
He can see a mile ahead and he got surprised by a roadblock... more than once...
I can get that he gave up on it and didn't bother always looking at it but why wouldn't he look ahead after that to see the landslide.