Good point brought up in the comment section about the SmallHD DP4 EVF 'not' having a lens cap to cover the glass. This could be tragic if you happen to leave it out in the sun. Since the SmallHD EVF uses standard 46mm threaded filters, the solution should be as simple as a basic lens cap available pretty much everywhere: Lens Cap for SmallHD Diopter
If you want one fast, there are a variety available on Amazon including some with Leica and Panasonic logos. They use the same 46mm size on many of their lenses (click here).
To make sure you prevent losing it and have it handy at all times, grab a set of very inexpensive lens cap keeper leashes (also good for your other lens caps) found below.
Lens Cap Keepers