Slander is not OK, but the answer is a civil suit in a court of law.
Treason and sedition are crimes and not something that ordinary citizens can legally enforce.
Tossing things at others is a crime. Preferably, the police will respond, but in some situations one may take action in reasonable self-defense or defense of others.
The leftists do use different rules than us, but we are not going to go down to their level.
Also, the "rules" or the behavior varies from leftist group to group. The Pinkos sent a couple whimps and a woman over to harass us the first time we countered them at Walter Reed: http://www.freerepublic.com/focus/f-news/1374288/posts However, they are relatively tame. It's the anarchists that you don't want to counter without heavy police presence, see http://www.freerepublic.com/focus/f-news/1326853/posts and read the "BARBARIANS AT THE GATES" section.
While I'm glad that there are those who counter the protests, I don't think that how I would deal with it, as it is more personal to me, since my family has shed blood in every war (since we were still colonies, or 10 generations, whichever you prefer).
Perhaps it's that there is the history of how they come prepared for "peaceful protest". We all know that the union thugs will join in on the fun sooner or later. Perhaps a few (Colt) Peacemakers might keep them in check.
You have your method which has a place, and I respect the fact you stand up for our military. I doubt I could maintain composure as well as shown by your group as I know the folks you are countering can get pretty rabid. If they get in my face and want to pi$$ on my vets graves, it would be another story (probably grab a headline or two during the dinner news hour). Maybe I am just geared up for their next phase already!
If I brought a heavy stick of hickory....is that acceptable as a "sign post"? Never can be "too prepared" when it comes to counter protest of leftie scumbags who don't have rules or have yet to have any enforced.