What does Father's Day MEAN to your husband? Does he want to be *honored*? Does he want the day *off*? Does he want to be recognized for his hard work throughout the year?
I would start there and that will point you in the right direction. (for example.... mom's who want to be *honored* want a gift, mom's who want a *duty free* day want b'fast in bed etc).
In my old age I'm becoming anti-gifts.... because I'm becoming anti-clutter.... and I'm old enough that I just look around and have too much stuff!!!!
Unless you know it's something he will LOVE it can become something he has to keep because someone gave it to him.
What's his fave food? Can father and son make it together? What's he always saying he wants to do.... but never gets around to? Spend 3 hours alone in the garage? Take Jr to the pool? Teach him to play golf so that every Father's Day from now on the two of them take off to go 18 holes?
I think Father's Day should be more about creating an "experience" that each remembers rather than adding a "thing" to your house.
That way your son can look back and say "every Father's Day my dad and I did xyz and it was cool". And your husband can do the same.