Unfortunately NVIS won't work with 2 meters because of the method of propagation and the layers of ionosphere that NVIS uses. NVIS is used primarily on 80, 60 and 40 meters.
If I was concerned about DFing on VHF, then I'd suggest a yagi antenna, with as many elements as you could realistically use. A 2 meter antenna with multiple elements would send a relatively tight beam, and if both stations were using yagis, you could reduce power and hopefully also reduce the chance of someone detecting your station. I would operate outside my AO and use a portable yagi, like this one
http://www.arrowantennas.com/arrowii/146-3ii.html Of course if you went the UHF route, then you would have yagis that have a smaller physical size, but you could have more gain with more elements. Arrow antenna makes VHF and UHF portable yagis, and I believe they'll also double as hiking sticks. They also make combination antennas for satellite work, so you could use both VHF and UHF, whichever would work best for your situation.