Best advice I can give is to get a tatoo of something that is relevant to you and that will remain so. This is a serious decision to modify your body, and if you are not 100% able to look at the design everyday until the day you die, don't do it.
Examples of tats that will be relevant:
Names of your children (they won't change, but you may not always be married to the same person...);
Family Coats of arms;
Regimental crests.