Rather than presume to know what you should do, I'll offer my praise for your asking what you should do, because you obviously know there's a problematic situation here with the dog (given your later comments in the thread).

I'd keep a very close and potentially harsh eye on the dog if it were mine.

Good intentions will always be pleaded for every assumption of authority. It is hardly too strong to say that the Constitution was made to guard the people against the dangers of good intentions. -- Daniel Webster