When searching for a unique birthday gift for your father it is leading to keep his personality and interests in mind. He is more than just dad. Bill Cosby has a great line; "Fatherhood is pretending the gift you love most is soap-on-a-rope."
Hopefully your leading goal is to make sure your father doesn't have to pretend that your gift is the many thing in the world. Think about your dad as his friends do for a minute. Think about him fishing or golfing. Think about hunting or some of his interests that are not because he is dad but as a man or an individual.
The more versatile a gift is the more likely you are going to get a look like Cosby describes. If you give a tie that says world's many dad, have you in fact plan very deeply about the gift?