Masuline cards in general are kind of make you think cards. I have several in my gallery. I have a non SU rollagraph wheel that has sailboats on it and have done about 3 similar yet different cards. Colors for cardstock make a huge difference. I like the old olive with the navy and the brilliant blue. They really pop together. I have also used stippled stencils block stamp to create backgrounds on cards then added simple package hand happy birthday (you could sub happy father's day.) Also pinecones are great. I helped my daughter make a card for her dad's birthday with black cs, a large pinecone stamped and embossed then a second layer with a center torn out to show the pinecone. Add some wire and beads. It was a neat card and she picked the colors.
What about frogs or dragonflies? Done in the right colors they are masculine too. And leaves are always a good choice.
Gallery at Splitcoaststampers
Gallery at Splitcoaststampers
Gallery at Splitcoaststampers
Gallery at Splitcoaststampers
Gallery at Splitcoaststampers
I hope that helps some. The Happy Father's Day stamp I used was non Su picked up out of a clearance basket, but it works!! Maybe this will give you a few ideas. My aunt has inspired me to work harder at "guy" cards as she's on a fixed income and has really been frustrated by what the cardstores have to offer. Fishing, golf and not much else.
Have a great day!!