Back at act 2, the road poneglyph wasn't found and suspected to be at onigashima.
However, at onigashima, law was seemed searching there for the road poneglyph, but to no avail.
What if kaido put the road poneglyph inside of his body? His dragon body serves as the greatest protection for it since that means the enemy would have to slice his body to get to the poneglyph, which would be very difficult to do.

However, at onigashima, law was seemed searching there for the road poneglyph, but to no avail.

What if kaido put the road poneglyph inside of his body? His dragon body serves as the greatest protection for it since that means the enemy would have to slice his body to get to the poneglyph, which would be very difficult to do.