I don't. We are ignoring it
Ignore it at your peril
You say that but Mrs S#2 and I have always ignored our anniversary. Having both been married before and gone through all the performance of "celebrating" something year after year which we knew was dying and ought to have been put out of its misery we felt that, second time around, we would be honest with one another and not celebrate the anniversary but simply accept that each were in the marriage because we wanted to be and that if either of us changed our minds we would go. It has worked so far, although family and friends do find it a bit odd that we don't "Go out for a meal" or even buy one another presents on the day. Still after 21 years we must be getting something right.
I buy her flowers when I feel like it and she will buy me a book or something for no particular reason. We prefer the spontaneity of showing our commitment and affection when we want to and not because it happens to be a certain date.
Another thing that people find odd about us is that we do not tell one another "I love you" parrot fashion. You know the way couples do. "Love you" pause "Love you too"
puke making. She may say "Love you" in passing and I'll just grunt to let her know I heard and at another time I may be the one that mentions the L word and she just smiles or grunts as the mood takes.
BUT mainly we are content in one another's company and we rub along quite happily.