AI'm making a beach scene cake and I need to write names in the sand. Any suggestions on doing that so the graham crackers don't shift around and fill in the writing?

Here is a photo of the cake I am replicating.

I would scratch the writing in the frosting - make the frosting sand coloured - and then cover ith a thin layer of 'sand'.

if your graham crackers are crushed pretty fine you should not have a problem.