Problem is that most will helicopter in to Camp David...assume? But, if there are limo's don't they still have to use a highway or road to get in from the airport? Perhaps staff will have to drive in.
I don't know logistics of Camp David...but, peaceful silent protests with hand held poster board signs might work if the protests could be situated in places where some of them can be seen.
I say hand held poster board signs because when George W. came to our state to meet with one of his big donors after the Iraq Invasion...we peace activists lined the roadway so his Black SUV convoy with him in the Presidential Limosene could be seen. Many had signs with stake holders and the police made us remove the stake holders because they said the stakes could be used as weapons. 
They did bring barracades to cage us but, we were close enough that we saw the Unitary Executive smirk at us through his tinted glass window. And, the whole entourage knew that there were protestors peacefully demonstrating.
If there is a town nearby Camp David perhaps a vigil could be held there if the roadways are shut down.
Just thoughts.
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