If you live and die through HDMI, then you might have heard a few stories (maybe experienced it yourself) about HDMI damage on your DSLR. This little achilles heel in DSLR workflow when using LCD monitors or EVF solutions can cost you big repair bills. Zacuto introduces a new HDMI lock (requires a zacuto plate to mount) called the Pincher. Not the cheapest solution, but it's almost the only one out there. Found at the Zacuto website, or a few dollars cheaper at B&H.
Zactuo HDMI Lock - Pincher
Or as some others have pointed out in the comments, the new TrusMT DSLR cage has HDMI locking options found here.
TrusMT DSLR Cage Ultimate with HDMI Locking
Earlier the item was out of stock, now it's back in and available. Found below if you've been waiting.
Zacuto EVF HDMI Electronic View Finder
Thanks to Joseph over at ShadowMindProductions.com for the tip on this $6 dollar HDMI splitter. Joseph mentions there's no video lag between monitors during his tests. Now you'll be able to use an external monitor for camera operator, and if you want, a larger one for the the director. I'm sure these are going to come in especially handy once those EVF - electronic view finders become the norm. This way you'll be able to frame and compose, while the EVF might help you focus a bit better. Here's the link: HDMI Male To 2 HDMI Female Splitter Adapter Cable