I'd probably have my people carry water balloons. Actually, that's what the assh*les were putting up for serious discussion, so that in and of itself should keep us from considering it.
Best thing to do, and DC Chapter is organizing a counter to their happy horse crap, it to be a better presence than them, and to get the story of who they are and what they did last time, desecrating the Navy Memorial, is a better use of our time.
Throwing a water balloon at a civilian on the sidelines is a minor infraction. Throwing a water balloon at a federal employee could get them in deep doo doo.
Have to admit though, most of these punks don't have the guts to carry out even a water balloon threat. The streets will be lined with police and military honor guard. I would not throw a water balloon at W with a Marine in my face. It might be my last conscious act in my life.