Just a mention, we only found out last year on accident. Veterans or Gold star families can get free lifetime passes at participating parks or you can fill out an online form and pay like a $10 processing fee. Lady noticed my wife and I were gonna pay for admission with our USAA cards, asked if one of us were vets (we both are) and started throwing pamphlets and stuff at us for the free lifetime pass.

Edit: Source for more information https://www.nps.gov/planyourvisit/veterans-and-gold-star-fam...