I never thought to tell my Dad and I regret that so have tried to make an effort to express my thanks going forward. I have a good friend who served for ~15 years and he mentioned that it sounds hollow at times hearing it, but at the same time he appreciates the thought.
Going forward... There are many cool ways to "show" your Dad that you appreciate the fact that he served for his country. The three things I did with my Dad until his death was: Visit a local military cemetery and place flowers on the graves of random military soldiers (lost in battle) or veterans that died years later after serving. Volunteer at a nearby Veterans hospital for a random one day with your Dad. Contact your local Reserves, National Guard, or Active Duty Base to do volunteer work with your Dad. I primarily live abroad now in another country with my family. Although my old man died many years ago...I still fly back to the states to do the above in honor of my father, grandfather, great-grandfather, and ancestors before them who all served. I make a special visit every year to Kentucky where my old man is buried. In addition, having served in the military in the past myself...if I see a Veteran (proud ones wear a veteran's symbol) or soldier in uniform standing in line in the grocery store...I will pay for their groceries. My mom to this day, a few days before veteran's day...will visit a elementary school near a military base and read children stories to help kids think of happy moments...same stories she read to my siblings and I when we were kids growing up in a military family. They will greatly appreciate the little things that you do for them on any random day of the year. It's an important display of respect especially when such is done with my own teenagers (one now in military school, one plans to be in ROTC in a few years) so that they understand the same respect regardless if it's a Veteran or Soldier of the United States, Canada, or France where we live. https://www.signupgenius.com/groups/veterans-day-activities-ideas.cfm By the way, this forum ET has Veterans that served. Unfortunately, there have been a few members here at ET outspoken against Veterans and/or targeted Veterans in general with derogatory comments about them or about the military while the insulting member pretends to be patriotic as someone expressing (free speech) their opinions about Veterans. I have those particular ET members (some active members) on ignore/block. wrbtrader