Dad, I hope you're having a wonderful day filled with everything that you enjoy and love. Though since you're currently hosting my 6-year daughter I'm pretty sure there is little time to yourself and even smaller amounts of energy to expend. Stay strong - I'm coming to get her soon.
But seriously, there is no gift or card that I can even imagine presenting you with that could come close to expressing my love and admiration for you. You and Mom combined to model and teach me so many of the lessons that have molded me into the man that I have become. I hope to become that kind of parent with my own children.