Kids do well with visuals rather than just saying Daddy/Mommy will be home in X amount of days. When we use these at my home, we keep a calendar next to them to mark off the days as well. That way we don't forget to switch any pebbles. Things can get pretty hectic when your spouse is deployed and it's easy to forget things like that.
I will include 365 pebbles bagged in quantities of 30 and 31 to help make it easy for you to adjust to your needs. You may choose to have them all the same color or mixed. For the name please specify Daddy, Mommy, or whatever nickname you may want on the vases. In this picture there are 214 pebbles, so if you will be using the full 365 it will be completely full.