Further to that, I must add that my father is a well respected and acknowledged expert on most things he considers 'offworld', and I was brought up with the knowledge that alien civilsations have existed and died millenia before homo sapiens evolved. So not only do I believe there are more advanced civilisations out there, but there have been and will be long after we are gone. Evidence for them arriving here once, let alone hundreds of times is absolute zero.
Has your father penned any books or scientific papers on the subject? How about his name, and I'll do a search on Amazon or on various academic-paper search engines I know?
Unfortunately, people believing what others tell them (and this is no way a slight on you or your father) is the fundemental basis for religion, and coincidentally suicide bombers!
Religion is basically believing peoples accounts of an event that they weren't even witness to themselves - which just so happens to neatly coincide with UFO stories.
I know a lot of people who firmly believe in Jesus Christ, even though the story of his birth on december 25th, 3 kings, star in the east, died for 3 days, was resurrected, all date back to 3,000BC (lookup the story of Horus). All of these facts have astronomical basis (and yes, I can provide evidence and links, which most importantly people can then investigate FOR THEMSELVES, rather than just believing me which is what I DON'T want.
However when you present people with this evidence, they become even more defensive and come up with the most outrageously flawed logic to try and explain their way out of it.
http://www.npr.org/templates/story/story.php?storyId=128490874
However, can anyone ever prove to others what they have seen?
No they can't, as proof itself requires the person being convinced of seeing it for themselves.
There is no question that there are a lot of people out there who firmly believe in UFO's - I believe that the mathematical odds being in favour of life out there somewhere, and I believe in UFO's - REAl UNIDENTIFIED FLYING OBJECTS. Not Alien's, but UFO's - ball lightning being one such phenomena.
Instead of simply believing others and passing on heresay, why not do some research, present it in a book with citations and evidence, and then we'll see shall we?