40th wedding anniversary invite

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I need an invitation for my parents 40th wedding anniversary party. I want it lively, colorful and humorous. After 40 years my parents still hold hands. My dad still grabs my mom's butt when he walks by her. My mom still affectionately bitches about the same things my dad does. and has done, for as long as i can remember. They actually still like being around each other after 40 years of births and deaths and relocations and losing a child and raising 2 other daughters and losing parents and doting on grandkids. They support each other; stand up for each other; and they RESPECT each other. I have had the great privilege to witnes first hand what a strong marriage actually looks like and anymore, that is rare. So I need a special invite acknowledging the awesomeness of 40 years of marriage

It's a surprise for my mom, my dad is planning it. He rented a boat with live music, food and booze. I want a unique, FUN invite bc they absolutely love life. I'm torn between a 1977 throw back invite or a more modern one, but either way I want it lively and UNIQUE.