dianebk,
Why would you think your dad's ghost be at the cemetery?
We are lead to believe by 'experts' that ghosts are tied to a certain locale (home, favorite hangout) or event(death).
Maybe the cemetery ghosts find it better to be there than home(been there).

Some paranormal investigators say a blessing or prayer after their investigations to request that the spirits stay there and not leave and form an attachment to them.

So I dun'no.