A nice, expensive bottle of his favorite libation. And you to follow....
A pair of tickets to his favorite sports team game if he is into sports.
a well-made and concealable weapon
On Father's Day, I get to do ANYTHING I want with my family. That could mean going out to a restaurant that no one likes but me (and they can't complain). I could choose a movie, attraction or event. Usually, I choose to go to a local park in the center of town and improvise music together. Sort of like busking without passing the hat. I have a blast doing it and it doesn't even cost any money.
Another favorite gift of mine is an Amazon.com gift certificate. They always have stuff I want.
Maybe a nice monogrammed leather wallet.
I got my guy a cigar cutter and lighter with his initials engraved on it. Going to give it to him before we go out to the cigar bar we like the next time we go.
A monogrammed dress shirt.
Depends what he is into. Classic pen, hip flask, chess set, nice belt, wallet............along those lines thinking you want it to be a pen that would last and mean a lot.
a good night away in a hotel??
Give him your undivided attention. That's free.
A silk tie, a white shirt with cuffs (maybe), strawberry booblube for him to use on you, a decent book about something he enjoys - cars, guns, ruby/soccer, or, something to listen to he has always wanted.
Hard to say--find out what he's really interested in and go from there. For me it would be books or DVDs or art or music supplies.